Dielectric filter having pairs of capacitive coupling windows between resonators and transceiver using the dielectric filter

ABSTRACT

A dielectric filter includes a plurality of dielectric blocks, each having a resonator therein, in which both the resonant frequency of each resonator and the degree of coupling between adjacent resonators are independently adjustable. The outer and inner surfaces of each dielectric block are coated with a thin film of a conductive material. Input and output electrodes are formed on the dielectric blocks by disposing a conductive film area on exposed areas of the blocks which are not coated with conductive film. Adjacent dielectric blocks are integrally bonded to one another via a conductive adhesive material and output coupling electrodes on the side surfaces of the dielectric blocks are bonded to input coupling electrodes on the side surfaces of adjacent dielectric blocks.

RELATED APPLICATIONS

This is a Continuation of application Ser. No. 08/662,503 filed Jun. 13,1996, now abandoned, which is a Continuation of application Ser. No.08/423,044, filed Apr. 4, 1995, now abandoned, which is a DivisionalApplication of 08/089,223, filed Jul. 8, 1993, now abandoned.

FIELD OF THE INVENTION

The present invention relates to a dielectric filter consisting of aplurality of dielectric blocks and a transceiver using the dielectricfilter.

PRIOR ART

In a conventional dielectric filter of the kind referred to above, thereare provided a plurality of resonators in a hexahedral rectangulardielectric unit. All of the six surfaces of the filter are substantiallycoated with an electrode film, and therefore, the filter does notrequire a shielding case or a mounting bracket, that is, the filter isof a model able to be mounted on the surface of a circuit board. In theconventional structure as above, since a plurality of resonators areprovided in one dielectric block, many different types of molds must beprovided if filters of a different number of resonators are desired.More specifically, as the dielectric filter of this type is generallyformed of ceramic material, the dielectric filter is manufactured byplacing powders of ceramic material in a mold and baking the mold.Therefore, a different mold must be prepared for each type of filter tobe manufactured, thus raising manufacturing costs. Moreover, since thedistance between the resonators is determined by the size and shape ofeach mold, the degree of coupling between the resonators is hard to set.

In another example of a conventional dielectric filter of a comb linetype, the degree of coupling of the resonators and the frequency of eachresonator are interrelated as a function of the structure of the filter.One is changed when the other is changed, and the other is automaticallydetermined as one is determined, and therefore it is difficult toadjust, the resonant frequency and the degree of coupling independentlyof each other.

In a further example of a known dielectric filter, one resonator isprovided in a single dielectric block which is coupled with anotherdielectric block having a resonator. Since a separate element is used tocouple the dielectric blocks in this example, the structure iscomplicated and the number of parts is increased. This complicatesmanufacturing procedures and increases manufacturing costs.

Yet another known dielectric filter is composed of a plurality ofdielectric bodies, each of which is provided with a resonator and bondedtogether to form a unit. The resonator used is a quarter-wave resonatorwherein one end face is short circuited and the other end face is opencircuited. Electromagnetic energy leaks from the open circuited endface, leading to undesirable coupling of resonators. It is verydifficult to achieve a predetermined degree of coupling with thisstructure. Further, a shielding cover to prevent the undesired couplingwith an external circuit is required. There is also a limit to thedegree the transceiver can be miniaturized when this type of filter isemployed.

SUMMARY OF THE INVENTION

A central object of the present invention is to provide a noveldielectric filter which can be easily manufactured to be compact insize, with a variable number of resonators, which does not require abracket or a shielding case and which does not require different moldsfor each resonator. It is a further object of the present invention toreduce the number of components and reduce manufacturing costs. It is afurther object of the present invention, to provide a filter wherein theresonant frequency of each resonator and the degree of coupling betweenresonators can be independently set or adjusted as desired.

A transceiver according to the present invention is to be miniaturizedby using the dielectric filter of the present invention mentioned above.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a filter I according to a firstembodiment of the present invention;

FIG. 2 is a cross sectional view taken along the line A--A of FIG. 1;

FIG. 3 is a cross sectional view taken along the like B--B of FIG. 1;

FIG. 4 is an equivalent circuit diagram of the filter I of FIG. 1;

FIG. 5 is a development diagram of four side surfaces of a firstdielectric block 110 in FIG. 1;

FIG. 6 is a development diagram of four side surfaces of a second andthird dielectric block 120 in FIG. 1;

FIG. 7 is a development diagram of four side surfaces of a fourthdielectric block 140 in FIG. 1;

FIG. 8 shows a modified filter constructed by coupling the first andfourth dielectric blocks 110, 140 of FIG. 1;

FIG. 9 shows a modified filter constructed by coupling the first, secondand fourth dielectric blocks 110, 120 (130), 140 of FIG. 1;

FIG. 10 is a perspective view of a filter II according to a secondembodiment of the present invention;

FIG. 11 is a cross sectional view taken along the line D--D of FIG. 10;

FIG. 12 is a cross sectional view taken along the line F--F of FIG. 10;

FIG. 13 is an equivalent circuit diagram of the filter II of FIG. 10;

FIG. 14 is a development diagram of four side surfaces of a firstdielectric block 210 in FIG. 10;

FIG. 15 is a development diagram of four side surfaces of a second (andthird) dielectric block 220 (230) in FIG. 10;

FIG. 16 is a development diagram of four side surfaces of a fourthdielectric block 240 in FIG. 10;

FIG. 17 is a perspective view of a filter III according to a thirdembodiment of the present invention;

FIG. 18 is a cross sectional view taken along the line G--G of FIG. 17;

FIG. 19 is a cross sectional view taken along the line H--H of FIG. 17;

FIG. 20 is an equivalent circuit diagram of the filter III of FIG. 17;

FIG. 21 is a development diagram of four side surfaces of a firstdielectric block 310 in FIG. 17;

FIG. 22 is a development diagram of four side surfaces of a second (andthird) dielectric block 320 (330) in FIG. 17;

FIG. 23 is a development diagram of four side surfaces of a fourthdielectric block 340 in FIG. 17;

FIG. 24 is a perspective view of a filter IV according to a fourthembodiment of the present invention;

FIG. 25 is a cross sectional view taken along the line J--J of FIG. 24;

FIG. 26 is a cross sectional view taken along the line K--K of FIG. 24;

FIG. 27 is an equivalent circuit diagram of the filter IV of FIG. 24;

FIG. 28 is a development diagram of four side surfaces of a firstdielectric block 410 in FIG. 24;

FIG. 29 is a development diagram of four side surfaces of a second (andthird) dielectric block 420 (430) in FIG. 24;

FIG. 30 is a development diagram of four side surfaces of a fourthdielectric block 440 in FIG. 24;

FIG. 31 is a perspective view of a filter V according to a fifthembodiment of the present invention;

FIG. 32 is a cross sectional view taken along the line M--M of FIG. 31;

FIG. 33 is a cross sectional view taken along the line N--N of FIG. 31;

FIG. 34 is an equivalent circuit diagram of the filter V of FIG. 31;

FIG. 35 is a development diagram of four side surfaces of a firstdielectric block 510 in FIG. 31;

FIG. 36 is a development diagram of four side surfaces of a second (andthird) dielectric block 520 (530) in FIG. 31;

FIG. 37 is a development diagram of four side surfaces of a fourthdielectric block 540 in FIG. 31;

FIG. 38 is a perspective view of a filter VI according to a sixthembodiment of the present invention;

FIG. 39 is a cross sectional view taken along the line P--P of FIG. 38;

FIG. 40 is a cross sectional view taken along the line Q--Q of FIG. 38;

FIG. 41 is an equivalent circuit diagram of the filter VI;

FIG. 42 is a development diagram of four side surfaces of a firstdielectric block 610 in FIG. 38;

FIG. 43 is a development diagram of four side surfaces of a second (andthird) dielectric block 620 (630) in FIG. 38;

FIG. 44 is a development diagram of four side surfaces of a fourthdielectric block 640 in FIG. 38;

FIG. 45 is a perspective view of an electrode disposed only at thebottom surface of a polyhedral dielectric block 710;

FIG. 46 is a perspective view of a modification of FIG. 45;

FIG. 47 is a circuit diagram of a transceiver according to the presentinvention;

FIG. 48 is a characteristic diagram of the dielectric filter of FIG. 8consisting of two dielectric blocks with coupling electrodes of onesize;

FIG. 49 is a characteristic diagram of the dielectric filter of FIG. 8consisting of two dielectric blocks with coupling electrodes of theother size; and

FIG. 50 is a characteristic diagram of the dielectric filter of FIG. 8consisting of two dielectric blocks with coupling electrodes of theother different size.

EMBODIMENTS

Several embodiments of the invention will be described, in which likereference numerals indicate like elements and parts, and each elementand part is described in connection with at least one drawing in whichit appears.

First Embodiment

A first embodiment of the present invention will be depicted withreference to FIGS. 1 through 7.

A filter I shown in FIG. 1 is a unit consisting of first, second, thirdand fourth dielectric blocks 110, 120, 130 and 140, as an example of acapacitive coupling type resonator having one end short-circuited andthe vicinity of the other end open-circuited and which resonates, forinstance, with a length of 1/4λ.

FIGS. 2 and 3 are cross sectional views taken along the lines A--A andB--B of FIG. 1, respectively, and FIG. 4 is an equivalent circuitdiagram of the filter I. FIG. 5 is a development diagram of four sidesurfaces of the first dielectric block 110 of FIG. 1. FIGS. 6 and 7 aresimilar development diagrams of four side surfaces of the second (andthird) and fourth dielectric blocks 120 (130) and 140 of FIG. 1. FIG. 8illustrates a modified filter obtained by coupling the first and fourthdielectric blocks 110, 140. Meanwhile, the filter of FIG. 9 is a furthermodification resulting from coupling of the first, second (third) andfourth dielectric blocks 110, 120 (130) and 140 .

The first dielectric block 110 is formed of a dielectric material suchas ceramic dielectrics or the like in the configuration of a generallyrectangular parallelepiped, having a top surface, a bottom surface, afront end surface, a rear end surface, a left side surface and a rightside surface. An opening 111 is bored passing through the central partof the first dielectric block 110, which is open-circuited at the frontand rear end surfaces of the block thereby to define a first resonatorR1-1.

A conductive thin film 112 is coated over the whole outer surfaces ofthe six surfaces and the inner surface of the opening 111 of the firstdielectric block 110 except for some portions to be described later by aknown electrode film forming technique using a conductive material,e.g., silver or copper. The conductive coating 112 at four of the sixsurfaces of the first dielectric block 110, namely, the top surface,bottom surface, right side surface and left side surface is formed asshown in the development diagram of FIG. 5. As is clear from FIG. 5, anexposed rectangular part where the conductive film is not coated therebyto expose the dielectric block is provided on the right side surface andthe bottom surface of the dielectric block in an area where the electricfield assumes its predominant energy component. An island in the exposedpart, having the conductive film coated thereon, is used as a firstinput coupling electrode 113. Similarly, a rectangular exposed partwithout the conductive film coated where the dielectric block is exposedis formed at the left side surface of the dielectric block, morespecifically, in an area where the energy component of the electricfield predominates, and an island in the exposed part where theconductive film is coated is used as a first output coupling electrode114. Moreover, as indicated in FIG. 2, an exposed part 115 where thedielectric block is exposed is provided in the inner surface of theopening at the closer side to the front surface of the block, where theexposed part 115 is a ring shape of small width not coated with theconductive film.

In the first dielectric block 110 constructed in the above-describedmanner, as represented in the equivalent circuit diagram of FIG. 4, theresonator R1-1 is defined by the opening 111 of the dielectric block. Anexternal coupling capacitance Ce is formed between the inner surface ofthe opening 111 and the right side surface and the bottom surface of theblock 110, while an internal coupling capacitance C1-1 is formed betweenthe inner surface of the opening 111 and the left side surface of theblock. That is, the first dielectric block 110 has the first inputcoupling electrode 113 as an input terminal of the filter I on the rightside surface and bottom surface thereof to couple an input signal withthe resonator R1-1, and the first output coupling electrode 114 at theleft side surface of the dielectric body. Further, a stray capacitanceCs is formed at the exposed part 115 of the inner surface of the opening111 where the dielectric block is exposed in the ring-shaped form.

The second dielectric block 120 is formed of a dielectric material suchas ceramic dielectrics or the like, having approximately the same sizeas the first dielectric block 110 in a generally rectangularparallelepiped with a top surface, a bottom surface, a front endsurface, a rear end surface, a left side surface and a right sidesurface. The second dielectric block 120 has also an opening 121 openedat the front and rear side surfaces thereof. The opening 121 penetratesthe central part of the block, constituting a second resonator R1-2.

The second dielectric block 120 is coated with a conductive thin film122 at the whole outer surfaces of the six surfaces and the innersurface of the opening 121 except for some portions to be describedlater, according to a well-known electrode film forming method using aconductive material, for example, silver or copper. The conductivecoating 122 at the top, bottom, right side and left side surfaces of thesecond dielectric block 120 is so formed as shown in the developmentdiagram of FIG. 6. More specifically, as is readily understood from FIG.6, a rectangular part where the dielectric block is exposed is providedat the right side surface of the block where the energy component of theelectric field is stronger, and the conductive film is not coated overthe exposed part, where an island with the conductive coating formed inthe exposed part is used as a second input coupling electrode 123.Meanwhile, another rectangular exposed part not coated with theconductive film is provided at the left side surface of the dielectricblock where the electric field has a superior energy component and anisland in the exposed part where the conductive film is coated becomes asecond output coupling electrode 124. At the same time, as shown in FIG.2, an exposed part 125 where the dielectric block is exposed without theconductive film is provided in the inner surface of the opening 121 atthe side closer to the front surface of the block, where the exposedpart 125 is ring-shaped and small in width.

As represented in the equivalent circuit diagram of FIG. 4, the opening121 of the second dielectric block 120 constitutes the resonator R1-2,and internal coupling capacitances C1-2 are defined respectively betweenthe inner surface of the opening 121 and the right side surface, andbetween the inner surface of the opening 121 and the left side surfaceof the block. In other words, the second input coupling electrode 123 isformed at the right side surface of the dielectric block so as to couplean input signal to the resonator R1-2, and the second output couplingelectrode 124 is formed at the left side surface of the block. A straycapacitance Cs is formed at the ring-shaped exposed part 125 in theinner surface of the opening 121.

The third dielectric block 130 made of a dielectric material such asceramic dielectrics, etc. is generally formed in the configuration of arectangular parallelepiped, with approximately the same size as the first dielectric block 110. The third dielectric block 130 has six surfaces,namely, a top surface, a bottom surface, a front end surface, a rear endsurface, a left side surface and a right side surface, and isconstructed in the structure similar to that of the second dielectricblock 120. An opening 131 of the third dielectric block 130 isopen-circuited, passing through the central part of the block, at thefront and rear end surfaces of the block, which defines a thirdresonator R1-3.

The third dielectric block 130 is coated with a conductive thin film 132at the outer surfaces of the six surfaces and the inner surface of theopening 131 except for some portions to be described later according toa known electrode film forming method with the use o f silver or copper,etc. As shown in FIG. 6, a third input coupling electrode 133 is formedat an island coated with the conductive film in an exposed part at theright side surface of the dielectric block where the electric fieldassumes superior energy. Moreover, a third output coupling electrode 134is obtained in an island where the conductive film is coated in anexposed part at the left side surface of the dielectric block, namely,where the energy component of the electric field is strong. Moreover, asindicated in FIG. 2, a ring-shaped exposed part 135 of small width wherethe dielectric block is exposed is provided in the inner surface of theopening 131 at the side closer to the front side surface of the block.

As represented in the equivalent circuit diagram of FIG. 4, in the thirddielectric block 130 of the above-described structure, the resonatorR1-3 is defined by the opening 131 of the dielectric body, whileinternal coupling capacitances C1-3 are secured between the innersurface of the opening 131 and the right side surface of the block, andthe inner surface of the opening 131 and the left side surface of theblock. That is, the second input coupling electrode 133 is formed at theright side surface of the dielectric block so as to couple an inputsignal with the resonator R1-3, and the third output coupling electrode134 is formed at the left side surface of the dielectric block. A straycapacitance Cs is defined at the exposed part 135 of the inner surfaceof the opening 131.

The fourth dielectric block 140 is made of a dielectric material, e.g.,ceramic dielectrics or the like, which is a generally rectangularparallelepiped and is approximately the same in size as the firstdielectric block 110, having a top surface, a bottom surface, a frontend surface, a rear end surface, a left side surface and a right sidesurface. Moreover, an opening 141 is bored to pass through the centralpart of the block and open-circuited at the front end and rear endsurfaces of the block 140, where the opening 141 constitutes a fourthresonator R1-4.

The fourth dielectric block 140 is coated with a thin conductive film142 at the outer surfaces of all the six surfaces and the inner surfaceof the opening 141 except for some portions which will be describedlater, where the film is coated in a known electrode film forming mannerusing silver, copper or the like conductive material. The conductivefilm 142 at the four, i.e., top surface, bottom surface, right sidesurface and left side surface of the fourth dielectric block 140 isformed as shown in the development diagram of FIG. 7. As indicated inFIG. 7, a rectangular exposed part where the conductive film is notcoated and therefore the dielectric block is exposed is provided at theright side surface of the dielectric block in an area where the energycomponent of the electric field is predominant, and a fourth inputcoupling electrode 143 is obtained at an island coated with theconductive film in the exposed part. On the other hand, a fourth outputcoupling electrode 144 is formed at an island of a rectangular exposedpart on the left side surface and the bottom surface of the dielectricblock in an area displaying more intense energy component of theelectric field. Although the conductive film is not coated in theexposed part, the island is coated with the conductive film. As is shownin FIG. 2, also in the inner surface of the opening 141 is formed anexposed part 145 where the dielectric block is exposed without theconductive film coated, being formed closer to the front surface of theblock in the shape of a ring of small width.

In the above-depicted structure of the fourth dielectric block 140, asrepresented in the equivalent circuit diagram of FIG. 4, the opening 141of the dielectric block constitutes the resonator R1-4, while aninternal coupling capacity C1-4 is defined between the inner surface ofthe opening 141 and the right side surface of the block, and an externalcoupling capacitance Ce is formed between the inner surface of theopening 141 and the left side surface and the bottom surface. In otherwords, the fourth dielectric block 140 has the fourth input couplingelectrode 143 at the right side surface thereof to couple an inputsignal with the resonator R1-4 and the fourth output coupling electrodeas an output terminal of the filter I at the left side surface and thebottom surface thereof. A stray capacitance Cs is formed at thering-shaped exposed part 145 of the inner surface of the opening 141.

When the above four dielectric blocks 110, 120, 130 and 140 aresequentially aligned in the lateral direction in a manner that the leftside surface of the first dielectric block 110 confronts the right sidesurface of the second dielectric block 120, the left side surface of thesecond dielectric block 120 confronts the right side surface of thethird dielectric block 130, and the left side surface of the thirddielectric block 130 faces the right side surface of the fourthdielectric block 140, and the dielectric blocks 110, 120, 130 and 140are bonded integrally via a conductive adhesive material, resulting inthe unit shown in FIG. 1, namely, the filter I of a type having one endshort-circuited and the vicinity of the other end open-circuited. Theequivalent circuit of the filter I has, as shown in FIG. 4, the fourresonators R1-1, R1-2, R1-3 and R1-4 which are connected via every twointernal coupling capacitances C1-1, C1-2, C1-3, and C1-4, with externalcoupling capacitances, Ce at both ends thereof. Each stray capacitanceCs in the equivalent circuit diagram of FIG. 4 is small enough to benegligible.

More specifically, the part 112 coated with the conductive film at theleft side surface of the first dielectric block 110, except for theportion where the dielectric block is exposed, is integrally bonded withthe part 122 coated with the conductive film at the right side surfaceof the second dielectric block 120 adjacent to the first dielectricblock 110, via a conductive bonding material 150, for example, a solder,a conductive adhesive containing silver powders, etc. Moreover, thefirst output coupling electrode 114 at the left side surface of thefirst dielectric block 110 is integrally bonded with the correspondingsecond input coupling electrode 123 at the right side surface of thesecond dielectric block 120 via the conductive material 150.

The part 122 coated with the conductive film at the left side surface ofthe second dielectric block 120 is integrally bonded with the part 132coated with the conductive film of the right side surface of theadjacent third dielectric block 130 via the conductive bonding material,and further the second output coupling electrode 124 at the left sidesurface of the second dielectric block 120 is bonded integrally to thethird input coupling electrode 133 at the right side surface of thethird dielectric block 130 via the conductive adhesive material 150.

The part 132 coated with the conductive film at the left side surface ofthe third dielectric block 130 is integrally bonded to the part 142coated with the conductive film at the right side surface of the fourthdielectric block 140, except for the exposed part, via the conductiveadhesive material 150. Moreover, the first output coupling electrode 134formed at the left side surface of the third dielectric block 130 isintegrally bonded to the second input coupling electrode 143 formedcorresponding to the electrode 134 at the right side surface of thefourth dielectric block 140, via the conductive adhesive material 150.

Second Embodiment

A second embodiment of the present invention will be discussedhereinbelow with reference to FIGS. 10 through 16.

A filter II of FIG. 10 is constituted of, first through fourthdielectric blocks 210, 220, 230 and 240 in a unit, which is an exampleof a capacitive coupling resonator with both ends short-circuited whichresonates, for instance, with a length of 1/2λ. In FIG. 10, the firstand fourth dielectric blocks 210 and 240 are shown by a solid line and,the second and third dielectric blocks are plotted by an imaginary line.

FIG. 11 is a cross section along the line D--D of FIG. 10, FIG. 12 is across section along the line F--F of FIG. 10, and FIG. 13 is anequivalent circuit diagram of the filter II. FIG. 14 shows a developmentdiagram of four side surfaces of the first dielectric block 210, FIG. 15and FIG. 16 being development diagrams of four side surfaces of thesecond (third) dielectric block 220 (230), and the fourth dielectricblock 240, respectively.

The first dielectric block 210 is formed of a dielectric material, forexample, ceramic dielectrics in the configuration of a generallyrectangular parallelepiped. The first dielectric block 210 has a topsurface, a bottom surface, a front end surface, a rear end surface, aleft side surface and a right side surface, where an opening 211spanning through the central part of the first block 210 isopen-circuited at the front and rear end surfaces of the block, therebyto constitute a first resonator R2-1.

In the first dielectric block 210, the outer surfaces of the sixsurfaces and the inner surface of the opening 211 are coated with a thinconductive film 212 by a well-known electrode film forming method usinga conductive material such as silver, copper or the like.

The conductive coating 212 at the top, bottom, right side and left sidesurfaces of the first dielectric block 210 is formed as developed inFIG. 14. As shown in FIG. 14, a rectangular part not coated with theconductive film where the dielectric block is exposed is provided at thebottom surface of the dielectric block in an area where a superiorenergy component of the electric field exists. An island in the exposedpart which is coated with the conductive film is used as a first inputcoupling electrode 213. Further, a rectangular part not coated with theconductive film where the dielectric block is exposed is formed at theleft side surface of the dielectric block where the electric field has asuperior energy component, and an island in the above part, but coatedwith the conductive film is a first output coupling electrode 214.

As represented in the equivalent circuit diagram of FIG. 13, the firstdielectric block 210 has a resonator R2-1 defined by the opening 211 o fthe dielectric body, while an external coupling capacitance Ce is formedbetween the inner surface of the opening 211 and the bottom surface ofthe block, while an internal coupling capacitance C2-1 is formed between the inner surface of the opening 211 and the left side surface ofthe block. In other words, the first dielectric block 210 has the firstinput coupling electrode 213 which is to serve as an input terminal ofthe filter II at the bottom surface of the dielectric block to couple aninput signal with the resonator R2-1, and has the first output couplingelectrode 214 at the left side surface of the dielectric block.

The second dielectric block 220 is made of a dielectric material, e.g.,ceramic dielectrics and generally formed in a rectangular parallelepipedof approximately the same size as the first dielectric block 210, havinga top surface, a bottom surface, a front end surface, a rear endsurface, a left side surface and a right side surface. An opening 221opened at the front and rear end surfaces of the second dielectric block220 penetrates the central part of the block, constituting a secondresonator R2-2.

The outer surfaces of the above six surfaces and the inner surface ofthe opening 221 of the second dielectric block 220 except for someportions to be described below are coated with a thin film of aconductive material 222 according to a known electrode film formingmethod with the use of a conductive material such as silver or copper.The conductive coating 222 at the top surface, bottom surface, rightside surface and left side surface of the second dielectric block 220 isformed as shown in the development diagram of FIG. 15. As is understoodfrom FIG. 15, an exposed part where the dielectric block is exposed isformed at the right side surface of the dielectric block where theenergy component of the electric field is strong. The rectangularexposed part is not coated with the conductive film. An island coveredwith the conductive film in the exposed part becomes a second inputcoupling electrode 223. There is a rectangular exposed part also at theleft side surface of the dielectric block in an area with the superiorenergy component of the electric field, which is not coated with theconductive film, and therefore the dielectric block is exposed. Anisland coated with the conductive film and formed in the exposed partbecomes a second output coupling electrode 224.

In the second dielectric block 220 in the above-described structure, asrepresented in the equivalent circuit diagram of FIG. 13, the resonatorR2-2 is defined by the opening 221 of the dielectric block, and internalcoupling capacitances C2-2 are formed between the inner surface of theopening 221 and the right side surface of the block, and between theinner surface of the opening 221 and the left side surface of the block,respectively. That is, the second dielectric block 220 is provided withthe second input coupling electrode 223 at the right side surface of theblock in order to couple an input signal with the resonator R2-2, alongwith the second output coupling electrode 224 at the left side surfaceof the block.

The third dielectric block 230 formed of a dielectric material such asceramic dielectrics or the like is generally a rectangularparallelepiped of approximately the same size as the first dielectricblock 210, having a top surface, a bottom surface, a front end surface,a rear end surface, a left side surface and a right side surface.Similar to the second dielectric block 220 in structure, the thirddielectric block 230 has an opening 231 open-circuited at the front endand rear end surfaces thereof through the central part of the block,where a third resonator R2-3 is defined by the opening 231.

The outer surfaces of the six surfaces and the inner surface of theopening 231 of the third dielectric block 230 except for some portionswhich will be explained later are coated with a conductive thin film 232by a well-known electrode film forming method with the use of aconductive material such as silver, copper or the like. As indicated inFIG. 15, a rectangular exposed part where the dielectric block isexposed without the conductive film coated is provided at the right sidesurface of the block in an area with superior energy component of theelectric field, and an island coated with the conductive film in theexposed part is a third input coupling electrode 233. Moreover, the leftside surface of the dielectric block with higher energy component of theelectric field is partly exposed and not coated with the conductivefilm. An island coated with the conductive film in the exposed part isused as a third output coupling electrode 234.

In the third dielectric block 230 in the above-depicted structure, as isclear from the equivalent circuit diagram of FIG. 13, the opening 231constitutes the resonator R2-3, and internal coupling capacitances C2-3are formed respectively between the inner surface of the opening 231 andthe right side surface and between the inner surface of the opening 221and the left side surface of the block. In other words, the thirddielectric block 230 has the second input coupling electrode 233 at theright side surface thereof to couple an input signal with the resonatorR2-3 and the third output coupling electrode 234 at the left sidesurface thereof.

The fourth dielectric block 240 is formed of a dielectric material, forexample, ceramic dielectrics, having a top surface, a bottom surface, afront end surface, a rear end surface, a left side surface and a rightside surface is a generally rectangular parallelepiped of approximatelythe same size as the first dielectric block 210. An opening 241 of thefourth dielectric block 240 is, passing through the central part of theblock, open-circuited at the front end and rear end surfaces of theblock, thus constituting a fourth resonator R2-4.

The fourth dielectric block 240 is covered with a thin conductive film242 at the outer surfaces of the six surfaces thereof and the innersurface of the opening 241, except for some portions to be describedlater, by a known electrode film forming method and a conductivematerial like silver, copper, etc. The conductive film 242 covering thetop surface, bottom surface, right side surface and left side surface ofthe fourth dielectric block 240 is formed in a manner as illustrated inthe development diagram of FIG. 16. As is clear in FIG. 16, arectangular part not coated with the conductive film where thedielectric block is exposed is provided at the right side surface of theblock in an area where the energy component of the electric field ispredominant. A fourth input coupling electrode 243 is obtained at anisland coated with the conductive film in the exposed part. Anotherrectangular part not coated with the conductive film where thedielectric block is exposed is formed at the bottom surface of the blockin an area showing more intense energy component of the electric field,and a fourth output coupling electrode 244 is formed at an island coatedwith the conductive film in the exposed part.

As indicated in the equivalent circuit diagram of FIG. 13, the resonatorR2-4 of the fourth dielectric block 240 is defined by the opening 241,and an internal coupling capacitance C2-4 is formed between the innersurface of the opening 241 and the right side surface of the block,while an external coupling capacitance Ce is formed between the innersurface of the opening 241 and the bottom surface of the block. In otherwords, the fourth input coupling electrode 243 of the fourth dielectricblock 240 is provided at the right side surface of the block so as tocouple an input signal with the resonator R2-4, and the fourth outputcoupling electrode 244 as an output terminal of the filter II is formedat the bottom surface of the block.

The above four dielectric blocks 210, 220, 230 and 240 are aligned inthe lateral direction so that the left side surface of the firstdielectric block 210 faces the right side surface of the seconddielectric block 220, the left side surface of the second dielectricblock 220 confronts the right side surface of the third dielectric block230, and the left side surface of the third dielectric block 230confronts the right side surface of the fourth dielectric block 240.When the dielectric blocks are bonded integrally to one another via aconductive adhesive material, the rectangular parallelepiped filter IIof FIG. 10 is obtained. In the equivalent circuit of the filter, asshown in FIG. 13, the resonators R2-1, R2-2, R2-3 and R2-4 are connectedvia every two internal coupling capacitances C2-1, C2-2, C2-3, and C2-4,and the external coupling capacitances Ce are provided at both ends ofthe filter.

More specifically, the part 212 coated with the conductive film at theleft side surface of the first dielectric block 210 is integrally bondedto the corresponding part 222 coated with the conductive film at theright side surface of the adjacent second dielectric block 220 exceptfor the exposed part by means of a conductive bonding material 250,e.g., a solder, a conductive adhesive containing silver powders or thelike, and the first output coupling electrode 214 formed at the leftside surface of the first dielectric block 210 is integrally bonded tothe second input coupling electrode 223 formed at the right side surfaceof the second dielectric block 220 via the conductive adhesive material250.

The part 222 coated with the conductive film at the left side surface ofthe second dielectric block 220 is integrally bonded to the part 232coated with the conductive film at the right side surface of the thirddielectric block 230 by the conductive adhesive material 250. At thesame time, the second output coupling electrode 224 at the left sidesurface of the second dielectric block 220 is integrally bonded to thethird input coupling electrode 233 formed at the right side surface ofthe third dielectric block 230 via the same conductive adhesive material250.

The part 232 coated with the conductive film at the left side surface ofthe third dielectric block 230 is integrally bonded to the part 242coated with the conductive film at the right side surface of the fourthdielectric block 240, except for the exposed part, via the adhesiveconductive material 250. The third output coupling electrode 234 at theleft side surface of the third dielectric block 230 is integrally bondedwith the fourth input coupling electrode 243 formed at the right sidesurface of the fourth dielectric block 240 via the conductive adhesivematerial 250.

Third Embodiment

FIGS. 17-23 represent a third embodiment of the present invention.

A filter III in FIG. 17 is formed of first through fourth dielectricblocks 310, 320, 330 and 340 which are combined in a single unit. Thefilter III is an example of a capacitive coupling resonatoropen-circuited in the vicinity of both ends thereof and resonating, forexample, with a length of 1/2λ. The first and fourth dielectric blocks310 and 340 are indicated by solid lines, while the second and thirddielectric blocks 320 and 330 are shown with imaginary lines in FIG. 17.

FIG. 18 is a cross sectional view taken along the line G--G of FIG. 17.FIG. 19 is a cross sectional view along the line H--H of FIG. 17. FIG.20 is an equivalent circuit diagram of the filter III. FIG. 21 shows adevelopment diagram of the four side surfaces of the first dielectricblock 310. FIG. 22 is a development diagram of four side surfaces of thesecond and third dielectric blocks 320 (330). FIG. 23 is a developmentdiagram of the fourth dielectric block 340.

Referring to FIGS. 17, 18 and 19 the, first dielectric block 310 is madeof a dielectric material, e.g., a ceramic dielectric, and has theconfiguration of a generally rectangular parallelepiped with a topsurface, a bottom surface, a front end surface, a rear end surface, aleft side surface and a right side surface. Moreover, the dielectricblock 310 has an opening 311 extending between the front and rear endsurfaces, where the opening 311 defines a first resonator R3-1 (FIGS. 19and 20).

Except for portions to be described later, the outer surfaces of theabove six surfaces and the inner surface of the opening 311 of the firstdielectric block 310 are coated with a thin film of a conductive coating312 according to a known electrode film forming method using aconductive material such as silver or copper. The conductive coating 312at the top surface, bottom surface, right side surface and left sidesurface of the first dielectric block 310 is formed as shown in thedevelopment diagram of FIG. 21. As shown in FIG. 21, a rectangularexposed area, where the dielectric block is exposed without theconductive film coating, is provided at the bottom surface of the blockin an area where the energy component of the electric field ispredominant, and a first input coupling electrode 313 is formed insidethe exposed area. Moreover, two additional exposed areas are provided atthe left side surface of the dielectric block in an area where theenergy component of the electric field is predominant. A pair of firstoutput coupling electrodes 314 (FIG. 21) are formed inside exposed areason the left side surface of the dielectric block. As is readilyunderstood from FIG. 18, there are also two ring-shaped exposed areas315 having a small width formed in the inner surface of the opening 311near the front and rear end surfaces of the dielectric block.

In the first dielectric block 310 of the above-discussed structure, asindicated in the equivalent circuit diagram of FIG. 20, the resonatorR3-1 is defined by the opening 311, and an external coupling capacitanceCe is formed between the inner surface of the opening 311 and the bottomsurface of the block, and an internal coupling capacitance C3-1 isdefined between the inner surface of the opening 311 and the left sidesurface of the block. In other words, the first input coupling electrode313 which is to be an input terminal of the filter III is provided atthe bottom surface of the block so as to couple an input signal with theresonator R3-1, while the first output coupling electrodes 314 areformed at the left side surface of the block. A pair of straycapacitances Cs are formed at the exposed ring-shaped parts 315 in theinner surface of the opening 311.

Referring to FIGS. 17, 18 and 19, the second dielectric block 320 isapproximately the same size as the first dielectric block 310, and isformed in the shape of a generally rectangular parallelepiped from adielectric material, such as a ceramic dielectric, with a top surface, abottom surface, a front end surface, a rear end surface, a left sidesurface and a right side surface. An opening 321 of the seconddielectric block 320 passes through the central part of the block to beopen-circuited at the front and rear end surfaces of the block, thusconstituting a second resonator R3-2 (FIGS. 19 and 20).

The outer surfaces of the six surfaces and the inner surface of theopening 321 of the second dielectric block 320 are coated with a thinconductive film 322 except for portions to be described below. Acommonly-used electrode film forming method using a conductive material,for example, silver or copper is employed to coat the film 322. Theconductive film 322 at the top surface, bottom surface, right sidesurface and left side surface of the second dielectric block 320 isformed as shown in the development diagram of FIG. 22. As indicated inFIG. 22, there are two rectangular areas at the right side surface ofthe block in an area of superior energy component of the electric field.Two input coupling electrodes 323 are formed in the exposed areas.Further, two output coupling electrodes 324 are provided at the exposedleft surface of the dielectric block in an area where the energycomponent of the electric field is high. As is clear from FIG. 18, thereare two further ring-shaped exposed areas 325 in the inner surface ofthe opening 321 near the front end and rear end surfaces of the block.

As represented by the equivalent circuit diagram of FIG. 20, theresonator R3-2 of the second dielectric block 320 is constituted by theopening 321, while internal coupling capacitances C3-2 are definedbetween the inner surface of the opening 321 and the right side surface,and between the inner surface of the opening 321 and the left sidesurface of the block. That is, the dielectric block 320 has the secondinput coupling electrodes 323 at the right side surface of the block soas to couple an input signal with the resonator R3-2, and the secondoutput coupling electrodes 324 at the left side surface of the block. Atthe same time, a pair of stray capacitances Cs are formed at the tworing-shaped exposed parts 325 in the inner surface of the opening 321.

Referring to FIGS. 17, 18 and 19, the third dielectric block 330 is agenerally rectangular parallelepiped formed of a ceramic dielectric orthe like of approximately the same size as the first dielectric block310. The third dielectric block 330 of a similar structure as the seconddielectric block 320, having a top surface, a bottom surface, a frontend surface, a rear end surface, a left side surface and a right sidesurface. An opening 331 passes through the central part of the block 330and is open-circuited at the front and rear end surfaces to define athird resonator R3-3 FIGS. 19 and 20.

The third dielectric block 330 is coated with a conductive thin film 332at the outer surfaces of the six surfaces and the inner surface of theopening 331 except for the part to be described below. The thin film 332is formed using a known electrode film forming method. As shown in FIG.22, two areas are exposed, each in the shape of a rectangle, in an areahaving a high energy component of the electric field. These two areasare located on the right side surface of the third dielectric block andare not coated with the conductive film. Two input coupling electrodes333 are formed on the exposed areas. In the same manner as above, twooutput coupling electrodes 334 are disposed at the left side surface ofthe dielectric block in an area where the electric field has apredominant energy component. As is clear from FIG. 18, two ring-shapedexposed areas 335 are provided on the inner surface of the opening 331near the front and rear side surfaces of the block. The exposed areas335 are not coated with the conductive film.

As indicated in the equivalent circuit diagram of FIG. 20, the opening331 defines the resonator R3-3, while two internal coupling capacitancesC3-3 are formed between the inner surface of the opening 331 and theright side surface and between the inner surface of the opening 331 andthe left side surface of the block, respectively. The third dielectricblock 330 has the third input coupling electrodes 333 at the right sidesurface thereof to couple an input signal to the resonator R3-3 and hasthe third output coupling electrodes 334 at the left side surfacethereof. A pair of stray capacitances Cs are formed at the two exposedareas 335 on the inner surface of the opening 331.

Referring to FIGS. 17, 18 and 19, the fourth dielectric block 340 ismade of a dielectric material, e.g., a ceramic dielectric or the like,and has a generally rectangular parallelepiped shaped of approximatelythe same size as the first dielectric block 310. The block 340 has a topsurface, a bottom surface, a front end surface, a rear end surface, aleft side surface and a right side surface. The fourth dielectric block340 has an opening 341 passing through the central part of the block 340and open-circuited at the front and rear end surfaces which forms afourth resonator R3-4 (FIGS. 19 and 20).

The fourth dielectric block 340 is coated with a thin conductive coatingfilm 342 on the six outer surfaces of the block 340 and on the innersurface of the opening 341, except for portions to be discussed below.The film 342 is formed using a known electrode film forming method. Thefilm 342 is made of a conductive material such as silver, or copper orthe like. The conductive coating film 342 at the top surface, bottomsurface, right side surface and left side surface of the block 340 is asshown in FIG. 23. There are two rectangular exposed areas which are notcoated at the right side surface of the dielectric block in an areahaving a high energy component of the electric field. Fourth inputcoupling electrodes 343 are disposed on the exposed areas. Further, arectangular exposed area is provided at the bottom surface of thedielectric block where a predominating energy component of the electricfield exists. This exposed area is not coated with the conductive film.A fourth output coupling electrode 344 is disposed on this exposed area.As indicated in FIG. 18, there are two ring-shaped exposed areas 345having a small width located near the front and rear side surfaces ofthe block on the inner surface of the opening 341.

As shown in the equivalent circuit diagram of FIG. 20, the fourthdielectric block 340 has an internal coupling capacity C3-4 between theinner surface of the opening 341 and the right side surface of the blockand an external coupling electrode 344 formed between the inner surfaceof the opening 341 and the bottom surface of the block. The fourthdielectric block 340 has the first input coupling electrode 343 at theright side surface thereof to couple an input signal to the resonatorR3-4. The fourth output coupling electrode 344, an output terminal ofthe filter III, is disposed on the bottom surface of the block. A pairof stray capacitances Cs are obtained at the ring-shaped exposed areas345 on the inner surface of the opening 341.

The above four dielectric blocks 310, 320, 330 and 340 are aligned sideby side such that the left side surface of the first dielectric block310 abuts the right side surface of the second dielectric block 320, theleft side surface of the second dielectric block 320 abuts the rightside surface of the third dielectric block 330 and the left side surfaceof the third dielectric block 330 abuts the right side surface of thefourth dielectric block 340. The dielectric blocks 310, 320, 330 and 340are integrally bonded via a conductive bonding material. Thus, thefilter III has a rectangular parallelepiped shape (FIG. 17). Theresonators R3-1 R3-2, R3-3 and R3-4 of the filter III are connected viainternal coupling capacitances C3-1, C3-2, C3-3 and C3-4 as shown in theequivalent circuit diagram of FIG. 20, and the external couplingcapacitances Ce are provided at both ends of the filter. It is notedthat the stray capacitances Cs are so small that they may be negligible.

More specifically, the part 312 coated with the conductive film at theleft side surface of the first dielectric block 310 is integrally bondedto the part 322 coated with the conductive film at the right sidesurface of the adjacent second dielectric block 320. However, theexposed part is bonded via a solder or conductive bonding material 350such as conductive adhesive containing silver powders. The first outputcoupling electrodes 314 at the left side surface of the first dielectricblock 310 are coupled to the second input coupling electrodes 323 at theright side surface of the second dielectric block 320 via the conductiveadhesive material 350.

The part 322 coated with the conductive film at the left side surface ofthe second dielectric block 320 is bonded to the part 332 coated withthe conductive film at the right side surface of the corresponding thirddielectric block 330 via solder or conductive adhesive material 350containing, for example, silver powders. The second output couplingelectrodes 324 at the left side surface of the second dielectric block320 are integrally bonded to the third input coupling electrodes 333formed at the right side surface of the third dielectric block 330 viasolder or conductive adhesive material 350 containing, for example,silver powders.

The part 332 (coated with the conductive film) is bonded at the leftside surface of the third dielectric block 330 to the part 342 (coatedwith the conductive film) at the right side surface of the adjacentfourth dielectric block 340 via solder or conductive adhesive material350 containing silver powders. The third output coupling electrodes 334are coupled at the left side surface of the third dielectric block 330to the corresponding fourth input coupling electrodes 343 formed at theright side surface of the fourth dielectric block 340 via solder orconductive adhesive material 350 containing silver powders.

Fourth Embodiment

A fourth embodiment of the present invention will be discussed withreference to FIGS. 24-30.

A filter IV in FIG. 24 consists of four blocks, i.e., first throughfourth dielectric blocks 410, 420, 430 and 440 in one unit, representingan example of an inductive coupling resonator having one endshorted-circuited and the vicinity of the other end open-circuited whichresonates, for instance, with a length of 1/4λ.

FIGS. 25 and 26 are cross sectional views respectively taken along theline J--J and K--K of FIG. 24, FIG. 27 indicates an equivalent circuitdiagram of the filter IV. FIG. 28 is a development diagram of four sidesurfaces of the first dielectric block 410 and FIG. 29 are developmentdiagrams of four side surfaces of the second and third dielectric blocks420 and 430, and FIG. 30 is a development diagram of four side surfacesof the fourth dielectric block 440.

The first dielectric block 410 is formed of a dielectric material, e.g,ceramic dielectrics or the like in a generally rectangularparallelepiped, having a top surface, a bottom surface, a front endsurface, a rear end surface, a left side surface and a right sidesurface. An opening 411 passing through the central part of the firstdielectric block 410 is open-circuited at the front and rear endsurfaces of the block thereby to constitute a first resonator R4-1.

The first dielectric block 410 is covered with a thin film of aconductive coat 412 at the outer surfaces of the above six surfaces andthe inner surface of the opening 411 except for some portions to bedescribed later, where a known electrode film forming method using aconductive material such as silver or copper is used to form the thinfilm. The conductive film 412 at the top surface, bottom surface, rightside surface and left side surface of the first dielectric block 410 isso formed as to be developed as illustrated in FIG. 28. As shown in FIG.28, a rectangular exposed part where the dielectric block is exposed andthe conductive film is not formed is provided in an area where theenergy component of the electric field is predominant, i.e., it isprovided on the right side surface and the bottom surface of thedielectric block. A part in the shape of an island in the exposed partand coated with the conductive film, is used as a first input couplingelectrode 413.

At the same time, a rectangular exposed part is secured in an areashowing superior energy component of the magnetic field a t the leftside surface of the dielectric block where the dielectric block isexposed without the conductive film coated, to obtain a magnetic fieldcoupling window which serves as an inductive coupling window 414.Further, as shown in FIG. 25, a ring-shaped exposed part of small widthis formed in the inner surface of the opening 411 at the closer side tothe front surface of the dielectric block, which is exposed at theexposed part 415. As illustrated in the equivalent circuit diagram ofFIG. 27, the first dielectric block 410 of the aforementioned structurehas the resonator R4-1 formed of the opening 411, with the externalcoupling capacitance Ce between the inner surface of the opening 411,and the right side surface and bottom surface of the block and, theinductive coupling window 414 at the left side surface of the block.Therefore, the first dielectric block 410 has the first input couplingelectrode 413 to be an input terminal of the filter IV at the right sidesurface and the bottom surface to couple an input signal with theresonator R4-1 and the first output coupling window 414 at the left sidesurface thereof. A stray capacitance Cs is formed at the ring-shapedexposed part 415 of the inner surface of the opening 411.

The second dielectric block 420 is made of a dielectric material, suchas a ceramic dielectric, etc. and has a top surface, a bottom surface, afront end surface, a rear end surface, a left side surface and a rightside surface in a generally rectangular parallelepiped of approximatelythe same size as the first dielectric block 410. The second dielectricblock 420 has an opening 421 open-circuited at the front end and rearend surfaces thereof which penetrates the central part of the block, andthe opening 421 forms a second resonator R4-2.

A conductive thin film 422 is coated by a known electrode film formingtechnique at the outer surfaces of the six surfaces and the innersurface of the opening 421 of the second dielectric block 420, exceptfor some portions to be described later, where a conductive material,e.g., silver or copper is used in the film forming method. Theconductive film 422 at the top surface, bottom surface, right sidesurface and left side surface of the second dielectric block 420 are soformed as to be developed as shown in FIG. 29. More specifically, as inFIG. 29, the dielectric block is exposed at a rectangular part at theright side surface thereof, specifically in an area where the magneticfield is the predominant energy component, and the dielectric block atthe exposed part is not coated with the conductive film, and the exposedpart is used as a second input coupling window 423 for the purpose ofinductive coupling. Another exposed part is formed in an area ofsuperior energy component of the magnetic field at the left side surfaceof the dielectric block 410 as well, where the rectangular exposed partis not coated with the conductive film and used as a second outputcoupling window 424 for inductive coupling. As indicated in FIG. 25, aring-shaped exposed part 425 of small width is also provided in theinner surface of the opening 421 at the side closer to the front sidesurface of the dielectric block, which is not coated with the conductivefilm.

The second dielectric block 420 is formed in the above-describedstructure as shown in the equivalent circuit diagram of FIG. 27, wherethe second dielectric block has the resonator R4-2 formed of the opening421, with the inductive coupling windows at the right side and left sidesurfaces of the dielectric block. That is, the second input couplingwindow 423 is formed at the right side surface of the dielectric blockto connect an input signal with the resonator R4-2, while the secondoutput coupling window 424 is formed at the left side surface of thedielectric block. Moreover, a stray capacitance Cs is obtained by thering-shaped exposed part 425 in the inner surface of the opening 421.

The third dielectric block 430 made of a dielectric material, forinstance, ceramic dielectrics, etc. is of approximately the same size asthe first dielectric block 410 and formed in a generally rectangularparallelepiped, with a top surface, a bottom surface, a front endsurface, a rear end surface, a left side surface and a right sidesurface. The third dielectric block 430 in the construction similar tothat of the second dielectric block 420 has an opening 431 opened at thefront and rear end surfaces thereof, and the opening 431 penetrates thecentral part of the dielectric block 430 to define a third resonatorR4-3.

The third dielectric block 430 is coated with a thin conductive film 432at the outer surfaces of the six surfaces and the inner surface of theopening 431 except for the part to be described later, while aconductive material such as silver or copper is used according to ageneral electrode film forming method. As shown in FIG. 29, arectangular part where the dielectric block is exposed and theconductive film is not coated is provided at the right side surface ofthe block in an area with superior energy component of the magneticfield, which works as a third input coupling window 433 for theinductive coupling. Moreover, a rectangular part where the dielectricblock is exposed and the conductive film is not coated is secured at theleft side surface of the block in an area of intense energy component ofthe magnetic field, to define a third output coupling window 434 for theinductive coupling, and additionally, a ring-shaped exposed part 435small in width is formed in the inner surface of the opening 431 at theside closer to the front side surface of the block, as in FIG. 25.

The third dielectric block 430 in the above constitution has, asrepresented in the equivalent circuit diagram of FIG. 27, the resonatorR4-3 constituted by the opening 431 and the inductive coupling windowsformed at the right side surface and the left side surface of the block.In other words, the third dielectric block has the third input couplingwindow 433 at the right side surface thereof to connect an input signalwith the resonator R4-3 and the third output coupling window 434 at theleft side surface thereof. At the same time, a stray capacitance Cs isformed at the ring-shaped exposed part 435 in the inner surface of theopening 431.

The fourth dielectric block 440 is made of a dielectric material, forexample, ceramic dielectrics and the like material, and is a generallyrectangular parallelepiped of approximately the same size as the firstdielectric block 410, having a top surface, a bottom surface, a frontend surface, a rear end surface, a left side surface and a right sidesurface. An opening 441 passing through the central part of thedielectric block 440 is open-circuited at the front and rear endsurfaces of the block thereby to constitute a fourth resonator R4-4.

The fourth dielectric block 440 is covered with a thin conductive film442 at the outer surfaces of the six surfaces and the inner surface ofthe opening 441 except for the part to be described later according to ageneral electrode film forming method with the use of a conductivematerial, for example, silver and copper. The conductive film 442 at thetop, bottom, right side and left side surfaces of the fourth dielectricblock 440 is so formed as to be developed as shown in FIG. 30. That is,a rectangular part is provided in an area of the superior energycomponent of the magnetic field at the right side surface of thedielectric block where the conductive film is not coated thereby toexpose the dielectric block, which functions as a fourth input couplingwindow 443 for the inductive coupling. Similarly, a rectangular exposedpart is provided on the left side surface and the bottom surface of thedielectric block in an area where the energy component of the electricfield is predominant, thereby to obtain a fourth output couplingelectrode 444 in the shape of an island. The fourth output couplingelectrode 444 is coated with the conductive film. Moreover, as shown inFIG. 25, a further exposed part 445 of small width is formed in theinner surface of the opening 441 at the closer side to the front sidesurface of the block, where the ring-shaped exposed part 445 is notcoated with the conductive film and therefore the di electric block isexposed.

As is clear in the equivalent circuit diagram of FIG. 27, the fourthdielectric block 440 of the above-discussed structure has the resonatorR4-4 defined by the opening 441 and is provided with the inductivecoupling window 443 at the right side surface, along with an externalcoupling capacity Ce between the inner surface of the opening 441, andthe left side surface and the bottom surface of the block. That is, thefourth input coupling window 443 is formed at the right side surface ofthe dielectric block to connect an input signal with the resonator R4-4and the fourth output coupling electrode 444 as an output terminal ofthe filter IV is located on the left side surface and the bottomsurface. A stray capacitance Cs is formed at the exposed part 445 in theinner surface of the opening 441.

The above four dielectric blocks are arranged laterally in a manner that the left side surface of the first dielectric block 410 is opposedto the right side surface of the second dielectric block 420, the leftside surface of the second dielectric block 420 facing to the right sidesurface of the third dielectric block 430, and the left side surface ofthe third dielectric block 430 to the right side surface of the fourthdielectric block 440. Then, when the dielectric blocks in the abovestate are bonded together via a conductive adhesive material, therectangular unit IV as shown in FIG. 24 is obtained as an example of afilter having one end short-circuited and the vicinity of the other endopened. In the equivalent circuit diagram of the unit of FIG. 27, fourresonators are connected via the inductive coupling windows and at thesame time, external coupling capacitances Ce are provided at both endsof the unit. Each stray capacitance Cs in FIG. 27 is as small asnegligible.

Specifically, the part 412 coated with the conductive film at the leftside surface of the first dielectric block 410 is bonded with the part422 coated with the conductive film at the right side surface of theadjacent second dielectric block 420 except for the exposed part bymeans of a conductive adhesive material 450 such as a solder, aconductive adhesive agent containing silver powers, etc. At the sametime, the first output coupling window 414 formed at the left sidesurface of the first dielectric block 410 which is not coated with theconductive film there by to expose the dielectric block is faced to theopposite second input coupling window 423 which is not coated with theconductive film at the right side surface of the second dielectric block420, thereby inductively coupling the resonators R4-1 and R4-2.

The part 422 coated with the conductive film at the left side surface ofthe second dielectric block 420 is, on the other hand, bonded integrallywith the part 432 which is coated with the conductive film at the rightside surface of the third dielectric block 430 adjacent to the secondblock 420, by the adhesive conductive material 450 such as a solder orconductive adhesive agent containing silver powders. Moreover, thesecond output coupling window 424 formed at the left side surface of thesecond dielectric block 420 is arranged to face the third input couplingwindow 433 at the right side surface of the third dielectric window 430,thereby to achieve the inductive coupling of the resonators R4-2 andR4-3.

The part 432 coated with the conductive film at the left side surface ofthe third dielectric block 430 is integrally bonded to the part 442coated with the conductive film at the right side surface of thecorresponding fourth dielectric block 440 adjacent to the thirddielectric block 430 except for the exposed part via the conductiveadhesive material 450 such as a solder or conductive adhesive agentcontaining silver powders, and the third output coupling window 434 atthe left side surface of the third dielectric block 430 is opposed tothe fourth input coupling window 443 formed at the right side surface ofthe fourth dielectric window 440 for the inductive coupling of theresonators R4-3 and R4-4.

Fifth Embodiment

A fifth embodiment of the present invention will now be described withreference to FIGS. 31-37.

A filter V of FIG. 31 is one unit composed of the first through fourthdielectric blocks 510, 520, 530 and 540, showing an example of aninductive coupling resonator resonating, for instance, with a length of1/2λ having both ends short-circuited.

FIG. 32 is a cross sectional view along the line M--M of FIG. 31 andFIG. 33 is a cross sectional view along the line N--N of FIG. 31, anequivalent circuit diagram of the filter V is shown in FIG. 34. FIGS.35, 36 and 37 respectively are development diagrams of four sidesurfaces of the first dielectric block 510, second (third) dielectricblock 520 (530) and fourth dielectric block 540.

The first dielectric block 510 is formed of a dielectric material, forexample, ceramic dielectrics. The shape of the first dielectric block510 is a generally rectangular parallelepiped having a top surface, abottom surface, a front end surface, a rear end surface, a left sidesurface and a right side surface, where an opening 511 penetrating thecentral part of the dielectric block 510 is open-circuited at the frontand rear end surfaces of the block to define a first resonator R5-1.

The first dielectric block 510 is coated with a conductive coating 512of a thin film by a known electrode film forming method with the use ofa conductive material such as silver, copper, etc., where the film iscoated over the outer surfaces of the above six surfaces and the innersurface of the opening 511 of the dielectric block except a part to bedescribed later. The conductive film 512 at the top, bottom, right sideand left side surfaces of the first dielectric block 510 is so formed asto be developed in a manner as shown in FIG. 35. As is apparent fromFIG. 35, there is an exposed rectangular part at the bottom surface ofthe dielectric block 510 in an area where the electric field displayssuperior energy component, which is not coated with the conductive filmand therefore the dielectric block is exposed, and an island in theexposed part which is coated with the conductive film is used as a firstinput coupling electrode 513. Moreover, a rectangular exposed part notcoated with the conductive film is further formed at the left sidesurface of the dielectric block in an area of the predominating energycomponent of the magnetic field, where a magnetic field coupling windowis open-circuited in the exposed part to be used as an inductivecoupling window 514.

The first dielectric block 510 in the construction as above has theresonator R5-1 defined by the opening 511. At the same time, an externalcoupling capacitance Ce is formed between the inner surface of theopening 511 and the bottom surface of the block, while the inductivecoupling window 514 is opened at the left side surface of the block, asshown in the equivalent circuit diagram of FIG. 34. Therefore, the firstinput coupling electrode 513 as an input terminal of the filter V isformed at the right side surface and bottom surface of the dielectricbody so as to couple an input signal with the resonator R5-1, and thefirst output coupling window 514 is provided at the left side surface ofthe dielectric block.

The second dielectric block 520 which is formed of a dielectric materialsuch as ceramic dielectrics in the shape of a generally rectangularparallelepiped of approximately the same size as the first dielectricblock 510, where an opening 521 of the second dielectric block 520 isopened at a front side and a rear side surfaces, passing through thecentral part of the block, thereby to constitute a second resonatorR5-2.

The outer surfaces of a top, a bottom, the front end, the rear end, aleft side and a right side surfaces of six surfaces of the dielectricblock 520 and the inner surface of the opening 521 are coated with athin conductive film 522 according to a generally-known electrode filmforming method using a conductive material, e.g., silver, copper or thelike. The conductive coating 522 at the top, bottom, right side and leftside surfaces of the block 520 is so formed as to assume the developmentdiagram shown in FIG. 36. A rectangular part which is not coated withthe conductive film is provided at the right side surface of thedielectric block 520 in an area of the predominant energy component ofthe magnetic field, and an island in the exposed part is used as asecond input coupling window 523 for the inductive coupling. At the leftside surface of the dielectric block where the magnetic field is thesuperior energy component is also formed a rectangular exposed part notcoated with the conductive film, where the exposed part is used as asecond output coupling window 524 for the inductive coupling.

As is clear from the equivalent circuit diagram of FIG. 34, the seconddielectric block 520 has the resonator R5-2 defined by the opening 521,with the inductive coupling windows formed respectively at the rightside and left side surfaces thereof. That is, the second input couplingwindow 523 is formed at the right side surface of the block to connectan input signal with the resonator R5-2, and the second output couplingwindow 524 at the left side surface of the block.

The third dielectric block 530 is made of a dielectric material such asceramic dielectrics, etc. in the shape of a generally rectangularparallelepiped of approximately the same size as the first dielectricblock 510, having a top surface, a bottom surface, a front end surface,a rear end surface, a left side surface and a right side surface. Thethird dielectric block 530 is in the similar structure to the seconddielectric block 520, i.e., having an opening 531 penetrating thecentral part of the block and open-circuited at the front and rear endsurfaces, thereby to form a third resonator R5-3.

The third dielectric block 530 is coated with a conductive thin film 532by a well-known film forming method using a conductive material such assilver, copper or the like. Specifically, the film is coated over theouter surfaces of the above six surfaces of the dielectric block 530 andthe inner surface of the opening 531, except for the part to be depictedlater. As shown in FIG. 34, a rectangular exposed part which is notcoated with the conductive film is secured at the right side surface ofthe dielectric block 530 in an area where the energy component of themagnetic field predominates to serve as a third input coupling window533 for the inductive coupling. Also, a rectangular part is exposed atthe left side surface of the dielectric block also in an area where theenergy component of the magnetic field is predominant, which is used asa third output coupling window 534 for the inductive coupling.

The third dielectric block 530 of the above-described construction is,as in the equivalent circuit diagram of FIG. 34, provided with theresonator R5-3 defined by the opening 531 and the inductive couplingwindows at the right side and left side surfaces thereof, namely, thethird input coupling window 533 at the right side surface to couple aninput signal with the resonator R5-3 and the third output couplingwindow 534 at the left side surface.

The fourth dielectric block 540 is formed of a dielectric material suchas ceramic dielectrics and the like in the shape of a generallyrectangular parallelepiped having approximately the same size as thefirst dielectric block 510 with top, bottom, front end, rear end, leftside and right side surfaces. The fourth dielectric block 540 has anopening 541 opened at the front and rear end surfaces thereof throughthe central part, thus constituting a fourth resonator R5-4.

The outer surfaces of the six surfaces and the inner surface of theopening 541 of the fourth dielectric block 540 except for some portionsto be described later are coated with a thin conductive film 542 by aknown electrode film forming method with using silver, copper and thelike conductive material. The conductive film 542 at the top, bottom,right side and left side surfaces of the fourth dielectric block 540 isso formed as to be developed into FIG. 37. That is, a rectangular partis exposed at the right side surface of the block in an area withsuperior energy component of the magnetic field, which is not coatedwith the conductive film thereby to expose the dielectric block, asshown in FIG. 37, and this exposed part is used as a fourth inputcoupling window 543 for the inductive coupling. At the same time, arectangular exposed part is provided at the bottom surface of the fourthdielectric block. An island in the exposed part, coated with theconductive film, is used as a fourth output coupling electrode 544.

In the fourth dielectric block 540 constituted in the above manner, theresonator R5-4 is formed of the opening 541 and the inductive couplingwindow 543 is opened at the right side surface, and an external couplingcapacitance Ce is provided between the inner surface of the opening 541and the bottom surface of the block. The fourth input coupling window543 formed at the right side surface of the dielectric block is tocouple an input signal with the resonator R5-4, and the fourth outputcoupling electrode 544 at the bottom surface of the dielectric blockworks as an output terminal of the filter V.

The above four dielectric blocks are aligned laterally so that the leftside surface of the first dielectric block 510 confronts the right sidesurface of the second dielectric block 520 and sequentially, the leftside surface of the second dielectric block 520 to the right sidesurface of the third dielectric block 530, the left side surface of thethird dielectric block 530 to the right side surface of the fourthdielectric block 540, and bonded one another by a conductive bondingmaterial. As a result, the filter V of one rectangular parallelepipedunit as shown in FIG. 31 is obtained. In the equivalent circuit diagramof the filter of FIG. 34, four resonators are connected via respectiveinductive coupling windows, and the external coupling capacitances Ceare present at both ends.

In other words, the part 512 coated with the conductive film at the leftside surface of the first dielectric block 510 is bonded to thecorresponding part 522 coated with the conductive film at the right sidesurface of the second dielectric block 520 except for the exposed partby means of a solder or a conductive bonding material 550 such as aconductive adhesive agent containing silver powders. Moreover, the firstoutput coupling window 514 at the exposed part of the left side surfaceof the first dielectric block 510 is faced to the second input couplingwindow 523 formed at the exposed part at the right side surface of thesecond dielectric block 520, thereby to achieve the inductive couplingof resonators R5-1 and R5-2.

The part 522 coated with the conductive film at the left side surface ofthe second dielectric block 520 is integrally bonded to the part 532coated with the conductive film at the right side surface of the thirddielectric block 530 adjacent to the second dielectric block 520 via theconductive adhesive material 550 such as a solder or conductive adhesiveagent containing silver powders, and the second output coupling window524 at the left side surface of the second dielectric block 520 isbrought to confront the third input coupling window 533 formed at theright side surface of the third dielectric block 530, thereby achievingthe inductive coupling of resonators R5-2 and R5-3.

The part 532 coated with the conductive film at the left side surface ofthe third dielectric block 530 is bonded to the corresponding part 542coated with the conductive film at the right side surface of the fourthdielectric block 540 except for the exposed part via the conductiveadhesive material 550 such as a solder or conductive adhesive agentcontaining silver powders. Moreover, the third output coupling window534 formed at the left side surface of the third dielectric block 530 isfaced to the fourth input coupling window 543 at the right side surfaceof the fourth dielectric block 540 to realize the inductive coupling ofresonators R5-3 and R54.

Sixth Embodiment

A filter according to a sixth embodiment of the present invention willbe described with reference to FIGS. 38-44.

A filter VI shown in FIG. 38 is one unit of four filters, includingfirst through fourth dielectric blocks 610, 620, 630 and 640,exemplifying an inductive coupling resonator having the vicinity of bothopen-circuited ends and resonating, for instance, with a length of 1/2λ.

FIG. 39 and FIG. 40 are cross sectional views taken along the lines P--Pand Q--Q of FIG. 38, respectively. FIG. 41 is an equivalent circuitdiagram of the filter VI, and FIGS. 42, 43 and 44 are developmentdiagrams of the four side surfaces of each of the first, second (third)and fourth dielectric blocks 610, 620 (630) and 640.

The first dielectric block 610 is made of a dielectric material, e.g., aceramic dielectric or the like, in a generally rectangularparallelepiped shape having a top side surface, a bottom side surface, afront end surface, a rear end surface, a left side surface and a rightside surface. The first dielectric block 610 has an opening 611 (FIG.40) passing through the central part thereof which is extended to thefront and rear end surfaces of the dielectric block 610, to constitute afirst resonator R6-1 FIG. 41.

Except for the areas described below, the six outer surfaces of thefirst dielectric block 610 and the inner surface of the opening 611 arecoated with a thin film of a conductive coating 612 by a known electrodefilm forming method with the use of a conductive material such assilver, copper, etc. The conductive coating 612 at the top surface,bottom surface, right side surface and left side surface of the block610 is formed in a manner as illustrated in the development diagram ofFIG. 42.

Specifically, as shown in FIG. 42, a rectangular exposed area (one whichis not coated with the conductive coating film) is provided at thebottom surface of the dielectric block 610 in an area having predominantenergy component of the electric field. In the exposed area, a firstelectrode 613 is formed to define a first input coupling electrode 613to to couple an input signal as described in more detail below.Additionally, a rectangular exposed area, which is not coated with theconductive coating film, is formed at the left side surface of thedielectric block 610 in an area with superior energy component of themagnetic field, to define an inductive coupling window 614. Further, asshown in FIG. 39, two ring-shaped exposed areas 615, each having a smallwidth, provided at the inner surface of the opening 611 near the frontend and rear end surfaces of the block.

The first dielectric block 610 has a resonator R6-1 defined by theopening 611, with the external coupling capacitance Ce formed betweenthe inner surface of the dielectric block of the opening 611 and thebottom surface and, the inductive coupling window 614 at the left sidesurface thereof, as is clear from the equivalent circuit diagram of FIG.41. Therefore, the first dielectric block 610 is provided with the firstinput coupling electrode 613 as an input terminal of the filter VI atthe bottom surface to couple an input signal with the resonator R6-1 andthe first output coupling window 614 at the left side surface of thedielectric block. At the same time, stray capacitances Cs (FIG. 41)defined by the exposed areas 615 formed in the inner surface of theopening 611.

The second dielectric block 620 is formed of a dielectric material, forexample, a ceramic dielectric, and is approximately the same size as thefirst dielectric block 610 and has a generally rectangularparallelepiped shape. The block 620 has top, bottom, front end, rearend, left side and right side surfaces. An opening 621 penetrating thecentral part of the second dielectric block 620 extends to the front andrear end surfaces of the block, constituting a second resonator R6-2.

The second dielectric block 620 is covered with a thin conductive film622 at the outer surfaces of the six surfaces and the inner surface ofthe opening 621 except for the sections described below. A knownelectrode film forming method is employed to coat these surfaces using aconductive material such as silver or copper. The conductive film 622 atthe top, bottom, right side and left side surfaces of the dielectricblock 620 is so formed as shown in the development diagram of FIG. 43.As illustrated in FIG. 43, a large exposed rectangular area is formed atthe right side surface of the dielectric block in an area where themagnetic field has a strong energy component. The exposed area defines asecond input coupling window 623 for the inductive coupling. Similarly,an exposed rectangular area is provided at the left side surface of thedielectric block in an area of the superior energy component of themagnetic field. This defines a second output coupling window 624 for theinductive coupling. Further, as shown in FIG. 39, two ring shapedexposed areas 625 are formed in the inner surface of the opening 621near the front and rear end surfaces.

As represented in the equivalent circuit diagram of FIG. 41, the seconddielectric block 620 has the resonator R6-2 constituted by the opening621 and the inductive coupling windows respectively at the right sideand left side surfaces thereof. That is, the second input couplingwindow 623 which connect an input signal to the resonator R6-2 isprovided at the right side surface of the dielectric block, while thesecond output coupling window 624 is formed at the left side surface ofthe dielectric block. Stray capacitances Cs are obtained at tworing-shaped exposed areas 625 in the inner surface of the opening 621.

The third dielectric block 630 formed of a dielectric material, e.g., aceramic dielectric or the like is approximately the same size as thefirst dielectric block 610 and has a generally rectangularparallelepiped configuration with top, bottom, front end, rear end, leftside and right side surfaces.

The third dielectric block 630 has approximately the same structure asthe second dielectric block 620, having an opening 631 penetrating thecentral part of the block which extends to the front and rear endsurfaces of the block and thus constitutes a third resonator R6-3.

The outer surfaces of the above six surfaces and the inner surface ofthe opening 631 of the third dielectric block 630 are covered with athin conductive film 632 except for portions to be described below. Theconductive film is applied according to a known film forming methodusing a conductive material, e.g., silver or copper. As shown in FIG.43, an exposed rectangular area is provided at the right side surface ofthe dielectric block 630 in an area where the energy component of themagnetic field predominates. The exposed area is used as a third inputcoupling window 633 for the inductive coupling. A similar uncoatedrectangular area is provided as well at the left side surface of theblock in an area where the energy component of the magnetic field isstrong and is used as a third output coupling window 634. Moreover, asshown in FIG. 39, a pair of small ring shaped exposed areas 635 areprovided in the inner surface of the opening 631 near the front end andrear end surfaces of the block, respectively. As indicated in theequivalent circuit diagram of FIG. 41, the third dielectric block 630 inthe above-described structure has the resonator R6-3 constituted by theopening 631 and inductive coupling windows respectively at the rightside and left side surfaces thereof. In other words, the thirddielectric block 630 has the third input coupling window 633 at itsright side surface to connect an input signal with the resonator R6-3,and the third output coupling window 634 at its left side surface, withstray capacitances Cs formed at the exposed parts 645 in the innersurface of the opening 631.

The fourth dielectric block 640 is formed of a ceramic dielectric or alike dielectric material in the shape which has a generally rectangularparallelepiped of approximately the same size as that of the firstdielectric block 610. The fourth dielectric block 640 has a top surface,a bottom surface, a front end surface, a rear end surface, a left sidesurface and a right side surface. An opening 641 penetrating the centralpart of the fourth dielectric block 640 is open-circuited at the frontand rear end surfaces of the block thereby to define a fourth resonatorR6-4.

The fourth dielectric block 640 is coated with a thin conductive film642 by a common electrode film forming method with the use of silver orcopper, that is, a conductive material. Specifically, the outer surfacesof the six surfaces and the inner surface of the opening 641 except forthe part to be discussed below are coated with the conductive film. Thefilm 642 at the top, bottom, right side and left side surfaces of thefourth dielectric block 640 is so formed as shown in the developmentdiagram of FIG. 44, an exposed rectangular area is formed at the rightside surface of the dielectric block 640 in an area where the magneticfield shows superior energy component. The exposed area defines a fourthinput coupling window 643 for the inductive coupling. A further exposedrectangular area is provided at the bottom surface of the dielectricblock where the electric field is the predominant energy component. Anisland shaped electrode is formed in this exposed area to define afourth output coupling electrode 644. A pair of small ring-shapedexposed areas 645 are formed near the front and rear end surfacesrespectively in the inner surface of the opening 641, as illustrated inFIG. 39.

The fourth dielectric block 640 in the above constitution has, asrepresented in the equivalent circuit diagram of FIG. 41, the resonatorR6-4 defined by the opening 641, the inductive coupling window 643 atthe right side surface thereof and an external coupling capacitance Cebetween the inner surface of the opening 641 and the bottom end surface.The fourth input coupling window 643 is formed at the right side surfaceof the fourth dielectric block, and the fourth output coupling electrode644 to be an output terminal of the filter VI is formed at the bottomsurface of the dielectric block. Moreover, two stray capacitances Cs areformed at the ring-shaped exposed areas in the inner surface of theopening 641.

The four dielectric blocks constituted in the above-described manner arealigned side by side such that the left side surface of the firstdielectric block 610 face the right side surface of the seconddielectric block 620, the left side surface of the second dielectricblock 620 face the right side surface of the third dielectric block 630,and the left side surface of the third dielectric block 630 face theright side surface of the fourth dielectric block 640. When the alignedblocks are integrally bonded via a conductive adhesive material, thefilter VI having a rectangular parallelepiped shape as shown in FIG. 38is obtained. In the equivalent circuit diagram of the filter, the fourresonators are connected via respective inductive coupling windows,having external coupling capacitances Ce at both ends, as in FIG. 41.The stray capacitance Cs of FIG. 41 is so small as negligible.

Particularly, the conductive 612 film at the left side surface of thefirst dielectric block 610 is bonded to the conductive film 622 at theright side surface of the adjacent second dielectric block 620 exceptfor the exposed area by a solder or a conductive bonding material 650containing silver powders. At the same time, the first output couplingwindow 614 not coated with the conductive film and formed at the leftside surface of the dielectric block 610 is opposed to the second inputcoupling window 623 at the exposed part of the right side surface of thesecond dielectric block 620, so that the inductive coupling is achievedbetween the resonators R6-1 and R6-2.

The conductive film 622 at the left side surface of the seconddielectric block 620 is integrally bonded to the conductive film 632 atthe right side surface of the third dielectric block 630 through theconductive adhesive material 650 such as a solder or conductive adhesiveagent containing silver powders. At the same time, the second outputcoupling window 624 formed at the left side surface of the seconddielectric block 620 opposes the third input coupling window 633 at theright side surface of the third dielectric block 630, thereby realizingthe inductive coupling of the resonators R6-2 and R6-3.

Meanwhile, the conductive film 632 at the left side surface of the thirddielectric block 630 is integrally bonded with the conductive film 642at the right side surface of the fourth dielectric block 640 except forthe exposed area by the conductive adhesive material 650. The thirdoutput coupling window 634 at the left side surface of the thirddielectric block 630 is faced to the corresponding fourth input couplingwindow 643 at the right side surface of the fourth dielectric block 640,to achieve the inductive coupling of the resonators R6-3 and R6-4.

Although the filter in each of the foregoing embodiment includes fourdielectric blocks in a single unit, the present invention encompassesunits having greater or lesser number of dielectric blocks. For example,a unit may be formed by coupling the first and fourth, two dielectricblocks, or the first, second (or third) as an inter-stage resonator andfourth dielectric blocks. It is also possible to provide three or moreinter-stage resonators.

In the case where the filter is to be formed of the first and fourthdielectric blocks of the first embodiment as shown in FIG. 8, the filtershould be composed of the following parts:

1) A first dielectric block 110 in the rectangular parallelepiped shape,having a first surface, a second surface and at least a first side, asecond side and a third side surfaces, with a first resonator R1-1extending between the first and second surfaces;

2) A first input coupling means 113 as an input terminal of the filterpositioned at least at one of the first side and second side surfaces ofthe first dielectric block 110, and coupled electrostatically to thefirst resonator R1-1;

3) A first output coupling means 114 disposed at least at the third sidesurface of the first dielectric block 110 and electrostatically coupledto the first resonator R1-1;

4) A first coating means 112 of a conductive material substantiallycovering at least the first, second, first side, second side and thirdside surfaces of the first dielectric block 110, except for the partwhere the first input coupling means 113 and the first output couplingmeans 114 are provided;

5) A through-hole 111 having both ends opened at the first and secondsurfaces of the first dielectric block 110, with the side surfacethereof partly covered with the conductive material in the lengthwisedirection. One end of the conductive body is connected to the firstcoating means 112 and the other end thereof is electrically insulatedfrom the first coating means 112;

6) A second dielectric block 140 in the rectangular parallelepipedshape, having a first, a second and at least a first side, a second sideand a third side surfaces, with a second resonator R1-4 extendingbetween the first and second surfaces;

7) A second input coupling means 143 disposed at least at the third sidesurface of the second dielectric block 140 and electrostatically coupledto the second resonator R1-4;

8) A second output coupling means 144 as an output terminal of thefilter provided at least at one of the first and second side surfaces ofthe second dielectric block 140 and electrostatically coupled to thesecond resonator R1-4;

9) A second coating means 142 of a conductive material substantiallycovering at least the first, second, first side, second side and thirdside surfaces of the second dielectric block 140, except for the partwhere the second input coupling means and the second output couplingmeans are provided;

10) A through-hole 141 having both ends opened at the first and secondsurfaces of the second dielectric block 140, with the side surfacethereof being partly covered with the conductive material in thelengthwise direction. One end of the conductive body is connected to thesecond coating means 142, and the other end thereof is electricallyinsulated from the second coating means 142;

11) The first output coupling means 114 and the second input couplingmeans 143 include the conductive substance formed at the third sidesurface of the first dielectric block 110 and at the third side surfaceof the second dielectric block 140, while being electrically insulatedfrom the first coating means 112 of the conductive material formed atthe third side surface of the first dielectric block 110 and the secondcoating means 142 of the conductive material formed at the third sidesurface of the second dielectric block 140, respectively;

12) A connecting means (not shown) electrically connecting the firstoutput coupling means 114 and the second input coupling means 143; and

13) A fixing means (not shown) fixing the first dielectric block 110 andthe second dielectric block 140.

Three kinds of filters each consisting of two dielectric blocks in thestructure as above are prepared to measure the filteringcharacteristics. More specifically, each dielectric block is formed 12.0mm long, 3.0 mm high and 2.6 mm wide, and each coupling electrode (firstoutput coupling means 114 and second input coupling means 143) providedat the side surface of the block is 1.4 mm high with an area (1) 1.4×2.2mm², (2) 1.4×1.6 mm², and (3) 1.4×1.3 mm². The results are shown ingraphs of FIGS. 48, 49 and 50, respectively. As is clear from the graphsof the measuring data, it is understood that the frequency bandwidth isincreased as the area of the electrode is larger, thus realizing higherdegree of coupling.

If the filter is to be constituted of three or more dielectric blocks,i.e., first, second (or third) and fourth or more dielectric blocks inthe first embodiment, the filter should be composed of the followingparts, as shown in FIG. 9:

1) A first dielectric block 110 in the rectangular parallelepiped shape,having a first, a second and at least a first side, a second side and athird side surfaces, with a first resonator R1-1 extending between thefirst and second surfaces;

2) A first input coupling means 113 as an input terminal of the filterpositioned at least at one of the first side and second side surfaces ofthe first dielectric block 110 and electrostatically coupled to thefirst resonator R1-1;

3) A first output coupling means 114 arranged at least at the third sidesurface of the first dielectric block 110 and electrostatically coupledto the first resonator R1-1;

4) A first coating means 112 of a conductive material substantiallycovering at least the first, second, first side, second side and thirdside surfaces of the first dielectric block, except for the part wherethe first input coupling means 113 and the first output coupling means114 are provided;

5) A through-hole 111 having both ends open-circuited at the first andsecond surfaces of the first dielectric block 110, with the side surfacethereof partly covered with the conductive material in the lengthwisedirection. The conductive material has one end connected to the firstcoating means 112 and the other end electrically insulated from thefirst coating means 112;

6) A second (or third) dielectric block 120 (or 130) as an inter-stageresonator in the rectangular parallelepiped, having a first, a secondand at least a first side and a second side surfaces, with a second (orthird) resonator R1-2 (or R1-3) extending between the first and secondsurfaces;

7) A second (or third) input coupling means 123 (or 133) positioned atleast at the first side surface of the second (or third) dielectricblock 120 (or 130) and electrostatically coupled to the second (orthird) resonator R1-2 (R1-3);

8) A second (or third) output coupling means 124 (or 134) disposed atleast at the second side surface of the second (or third) dielectricblock 120 (or 130) and electrostatically coupled to the second (orthird) resonator R1-2 (or R1-3);

9) A second (or third) coating means 122 (or 132) of a conductivematerial substantially covering at least the first, second, first sideand second side surfaces of the second (or third) dielectric block 120(or 130), except for the part where the second (or third) input couplingmeans 123 (or 133) and the second (or third) output coupling means 124(or 134) are provided;

10) A through-hole 121 (or 131) having both ends open-circuited at thefirst and second surfaces of the second (or third) dielectric block 120(or 130), with the side surface thereof partly covered with a conductivematerial in the lengthwise direction. One end of the conductive materialis connected to the second (or third) coating means 122 (or 132) and theother end thereof is electrically insulated from the second (or third)coating means 122 (or 132);

11) A fourth dielectric block 140 in the shape of a rectangularparallelepiped, having a first, a second and at least a first side, asecond side and a third side surfaces, with an inter-stage resonatorR1-4 extending between the first and second surfaces;

12) An input coupling means 143 for coupling the resonator R1-4 with theresonator R1-2 (or R1-3) in the precedent stage, positioned at the thirdside surface of the dielectric block 140 for the resonator andelectrostatically coupled to the resonator R1-4;

13) An output coupling means 144 as an output terminal of the filter,disposed at one of the first side and second side surfaces of thedielectric block 140 for the resonator and electrostatically coupled tothe resonator R1-4;

14) A third coating means 142 of a conductive material substantiallycovering at least the first, second, first side, second side and thirdside surfaces of the dielectric block 140 for the resonator, except forthe part where the input coupling means 143 and the output couplingmeans 144 are provided;

15) A through-hole 141 having both ends open-circuited at the first andsecond surfaces of the dielectric block 140 for the resonator, with theside surface thereof partly covered with a conductive material in thelengthwise direction. The conductive material has one end connected tothe third coating means 143, and the other end electrically insulatedfrom the third coating means 142;

16) The first output coupling means 114 includes the conductivesubstance formed at the third side surface of the first dielectric block110, while being electrically insulated from the first coating means 112of the conductive material at the third side surface of the firstdielectric block 110. Moreover, the input coupling means 123 (or 133) ofthe inter-stage resonator R1-2 (or R1-3) which is to be coupled to thefirst resonator R1-1 among at least one inter-stage resonator includesthe conductive substance formed at the first side surface of thedielectric block 120 (or 130) for the inter-stage resonator, and iselectrically insulated from the second (or third) coating means 122 (or132) of the conductive material formed at the first side surface of thedielectric block 120 (or 130) for the inter-stage resonator;

17) The fourth input coupling means 143 includes the conductivesubstance formed at the third side surface of the fourth dielectricblock 140 and is electrically insulated from the fourth coating means142 of the conductive material at the third side surface of the fourthdielectric block 140. The output coupling means 124 (or 134) of theinter-stage resonator R1-2 (or R1-3) which is to be coupled to thefourth resonator among at least one inter-stage resonator includes theconductive substance formed at the second side surface of the dielectricblock 120 (or 130) for the inter-stage resonator, and electricallyinsulated from the second (or third) coating means 122 (or 132) of theconductive material formed at the second side surface of the dielectricblock 120 (or 130) for the inter-stage resonator;

18) A connecting means (not shown) electrically connecting the firstoutput coupling means 114 with the input coupling means 123 (or 133) ofthe inter-stage resonator R1-2 (or R1-3) which is to be coupled to thefirst resonator R1-1 among at least one inter-stage resonator;

19) A connecting means (not shown) electrically connecting the fourthinput coupling means 143 with the output coupling means 124 (or 134) ofthe inter-stage resonator R1-2 (or R1-3) which is to be coupled to thefourth resonator R1-4 among at least one inter-stage resonator;

20) A fixing means (not shown) fixing the first dielectric block 110 andthe dielectric block 120 (or 130) for the inter-stage resonator providedat least by one; and

21) A fixing means (not shown) fixing the fourth dielectric block 140and the dielectric block 120 (or 130) for the inter-stage resonatorprovided at least by one.

In any of the foregoing second-sixth embodiments, it is possible toconstitute a filter of two stages, three stages and five or more stagesby combining suitably the dielectric blocks for the inter-stageresonator.

Regarding the state of the input/output electrode to mount the filter toa circuit board, although such an electrode 713a as shown in FIG. 45that is provided only at the bottom surface of a polyhedral dielectricblock 710 may be used, it is possible to form an electrode 713b on thebottom surface and the side surface of the polyhedral dielectric block710 as illustrated in FIG. 46. In FIG. 45, the contact with outside isobtained only at the electrode 713a at the bottom surface of thedielectric block 710. On the other hand, in FIG. 46, it is realized atthe electrode 713b on the bottom surface and the side surface of thedielectric block 710.

The filter embodied in each of the foregoing examples can be widely usednot only as an inter-stage filter installed between amplifiers, but as atransmission filter and/or a receiving filter, for instance, atransmission filter interposed between a transmission circuit and anantenna of a transceiver (including a radio telephone, an automobiletelephone, an aeronautical telephone, a ship service telephone and aportable telephone), or a receiver filter between a receiver circuit andthe antenna of the transceiver, as indicated in FIG. 47. If the filterof the present invention is employed as the transmission filter Sbetween the transmission circuit T and antenna W or receiver filter Vbetween the receiver circuit R and antenna W, the transceiver is turnedcompact in size.

What is claimed is:
 1. A dielectric filter, comprising:a firstdielectric block having a through bore extending between first andsecond end faces thereof, said first dielectric block having a pluralityof side surfaces extending between said end faces, each of said sidesurfaces lying in a respective plane, substantially all of the surfacearea of said end faces, said side surfaces and said bore being coveredwith a first conductive film to define a first dielectric resonator; afirst coupling window disposed on a first one of said side surfaces ofsaid first dielectric block, said first coupling window being defined bya first area which is not covered by said first conductive film andhaving a first input electrode located in said first area for providingcapacitive coupling between an input signal applied to said first inputelectrode and said first dielectric resonator; a second coupling windowdisposed on a second one of said side surfaces of said first dielectricblock, said second coupling window being defined by a second area whichis not covered by said first conductive film and having a secondelectrode located in said second area; a second dielectric block havinga through bore extending between first and second end faces thereof,said second dielectric block having a plurality of side surfacesextending between said end faces, each of said side surfaces lying in arespective plane, substantially all of the surface area of said endfaces, said side surfaces and said bore being covered with a secondconductive film to define a second dielectric resonator; a thirdcoupling window disposed on a first one of said side surfaces of saidsecond dielectric block, said third coupling window being defined by athird area which is not covered by said second conductive film andhaving a third electrode located in said third area; and a fourthcoupling window disposed on a second one of said side surfaces of saidsecond dielectric block, said fourth coupling window being defined by afourth area which is not covered by said second conductive film andhaving a fourth electrode located in said fourth area; said first one ofsaid side surfaces of said second dielectric block abutting said secondone of said side surfaces of said first dielectric block; said secondcoupling window of said first dielectric block being in a positioncorresponding to said third coupling window of said second dielectricblock; said second electrode of said first dielectric block beingelectrically coupled to said third electrode of said second dielectricblock such that signals from said first dielectric resonator arecapacitively coupled to said second dielectric resonator, wherein atleast one of said coated through bores of said first and seconddielectric blocks includes a pair of ring shaped areas, said ring shapedareas being disposed near a respective end of said at least one bore,said pair of ring shaped areas of said at least one bore having noconductive film thereon, wherein at least one of said coated throughbores of said first and second dielectric blocks includes a pair of ringshaped areas, each of said ring shaped areas being disposed near arespective end face of said at least one bore, said pair of ring shapedareas of said at least one bore having no conductive film thereon. 2.The filter according to claim 1, wherein said second electrode of saidsecond coupling window includes a conductive film disposed on the secondside surface of said first dielectric block.
 3. The filter according toclaim 1, wherein said third electrode of said third coupling windowincludes a conductive film disposed on the first side surface of saidsecond dielectric block.
 4. The filter according to claim 1, whereinsaid second coupling window includes a conductive substance disposed onsaid second side surface of said first dielectric block and which iselectrically insulated from said conductive film of said firstdielectric block.
 5. The filter according to claim 1, wherein said thirdcoupling window includes a conductive substance disposed on said firstside surface of said second dielectric block and which is electricallyinsulated from said conductive film of said second dielectric block. 6.The filter according to claim 1, wherein said first dielectric block isa rectangular parallelepiped.
 7. The filter according to claim 1,wherein said second dielectric block is a rectangular parallelepiped. 8.The dielectric filter of claim 1, further comprising:a third dielectricblock having a through bore extending between first and second end facesthereof, said third dielectric block having a plurality of side surfacesextending between said end faces, each of said side surfaces lying in arespective plane, substantially all of the surface area of said endfaces, said side surfaces and said bore being covered with a thirdconductive film to define a third dielectric resonator; a fifth couplingwindow disposed on a first one of said side surfaces of said thirddielectric block, said fifth coupling window being defined by a fiftharea which is not covered by said third conductive film and having afifth electrode located in said fifth area; and a sixth coupling windowdisposed on a second one of said side surfaces of said third dielectricblock, said sixth coupling window being defined by an sixth area whichis not covered by said third conductive film and having a sixthelectrode located in said sixth area; said first one of said sidesurfaces of said third dielectric block abutting said second one of saidside surfaces of said second dielectric block; said fourth couplingwindow of said second dielectric block being in a position correspondingto said seventh coupling window of said third dielectric block; saidfourth electrode of said second dielectric block being electricallycoupled to said fifth electrode of said third dielectric block such thatsignals from said second dielectric resonator are capacitively coupledto said third dielectric resonator.
 9. The filter of claim 8, whereinsaid sixth electrode is an output electrode for an output signal coupledto said sixth electrode.
 10. The filter of claim 8, wherein said fourthcoupling window associated with said second dielectric block is disposedat a substantially maximum energy location of an electric fieldassociated with said second dielectric block.
 11. The filter of claim 8,wherein said fifth coupling window associated with said third dielectricblock is disposed at a substantially maximum energy location associatedwith an electric field of said third dielectric block.
 12. The filter ofclaim 8, wherein said side surfaces of each of said first, second andthird dielectric blocks extend in a direction generally parallel to thedirection of their respective through bores.
 13. The filter of claim 8,wherein at least one of said coated through bores of said first, secondand third dielectric blocks includes a pair of ring shaped areas, eachof said ring shaped areas being disposed near a respective end face ofsaid at least one bore, said pair of ring shaped areas of said at leastone bore having no conductive film thereon.
 14. The filter of claim 13,wherein said ring shaped areas define respective stray capacitances. 15.The filter of claim 8, further comprising:a seventh coupling windowdisposed on said second side surface of said first dielectric block,said seventh coupling window being defined by a seventh area which isnot covered by said second conductive film and having a seventhelectrode located in said seventh area; an eighth coupling windowdisposed on said first side surface of said second dielectric block,said eighth coupling window being defined by an eighth area which is notcovered by said second conductive film and having an eighth electrodelocated in said eighth area; a ninth coupling window disposed on saidsecond side surface of said second dielectric block, said ninth couplingwindow being defined by a ninth area which is not covered by said secondconductive film and having a ninth electrode located in said ninth area;and a tenth coupling window disposed on said first side surface of saidthird dielectric block, said tenth coupling window being defined by atenth area which is not covered by said third conductive film and havinga tenth electrode located in said tenth area; said seventh couplingwindow of said first dielectric block being in a position correspondingto said eighth coupling window of said second dielectric block; saidseventh electrode of said first dielectric block being electricallycoupled to said eighth electrode of said second dielectric block suchthat signals from said first dielectric resonator are capacitivelycoupled to said second dielectric resonator; said ninth coupling windowof said second dielectric block being in a position corresponding tosaid tenth coupling window of said third dielectric block; said ninthelectrode of said second dielectric block being electrically coupled tosaid tenth electrode of said third dielectric block such that signalsfrom said second dielectric resonator are capacitively coupled to saidthird dielectric resonator.
 16. The dielectric filter of claim 8,further comprising:a fourth dielectric block having a through boreextending between first and second end faces thereof, said fourthdielectric block having a plurality of side surfaces extending betweensaid end faces, each of said side surfaces lying in a respective plane,substantially all of the surface area of said end faces, said sidesurfaces and said bore being covered with a fourth conductive film todefine a fourth dielectric resonator; a seventh coupling window disposedon a first one of said side surfaces of said fourth dielectric block,said seventh coupling window being defined by a seventh area which isnot covered by said fourth conductive film and having a seventhelectrode located in said seventh area; and an eighth coupling windowdisposed on a second one of said side surfaces of said fourth dielectricblock, said eighth coupling window being defined by an eighth area whichis not covered by said fourth conductive film and having an eighthelectrode located in said eighth area; said first one of said sidesurfaces of said fourth dielectric block abutting said second one ofsaid side surfaces of said third dielectric block; said sixth couplingwindow of said third dielectric block being in a position correspondingto said seventh coupling window of said fourth dielectric block; saidsixth electrode of said third dielectric block being electricallycoupled to said seventh electrode of said fourth dielectric block suchthat signals from said third dielectric resonator are capacitivelycoupled to said fourth dielectric resonator.
 17. The filter of claim 16,wherein said eighth electrode is an output electrode for an outputsignal coupled to said twelfth electrode.
 18. The filter of claim 16,wherein said sixth coupling window associated with said third dielectricblock is disposed at a substantially maximum energy location associatedwith an electric field of said third dielectric block.
 19. The filter ofclaim 16, wherein said seventh coupling window associated with saidfourth dielectric block is disposed at a substantially maximum energylocation associated with an electric field of said fourth dielectricblock.
 20. The filter of claim 16, wherein said side surfaces of each ofsaid first, second, third and fourth dielectric blocks extend in adirection generally parallel to the direction of their respectivethrough bores.
 21. The filter of claim 16, wherein at least one of saidcoated through bores of said first, second, third and fourth dielectricblocks includes a pair of ring shaped areas, each of said ring shapedareas being disposed near a respective end face of said at least onebore, said pair of ring shaped areas of said at least one bore having noconductive film thereon.
 22. The filter of claim 21, wherein said ringshaped areas define respective stray capacitances.
 23. The filter ofclaim 16, further comprising:a ninth coupling window disposed on saidsecond one of said side surfaces of said first dielectric block, saidninth coupling window being defined by a ninth area which is not coveredby said first conductive film and having a ninth electrode located insaid ninth area; a tenth coupling window disposed on said first one ofsaid side surfaces of said second dielectric block, said tenth couplingwindow being defined by a tenth area which is not covered by said secondconductive film and having a tenth electrode located in said tenth area;an eleventh coupling window disposed on said second one of said sidesurfaces of said second dielectric block, said eleventh coupling windowbeing defined by an eleventh area which is not covered by said secondconductive film and having an eleventh electrode located in saideleventh area; a twelfth coupling window disposed on said first one ofsaid side surfaces of said third dielectric block, said twelfth couplingwindow being defined by a twelfth area which is not covered by saidthird conductive film and having a twelfth electrode located in saidtwelfth area; a thirteenth coupling window disposed on said second oneof said side surfaces of said third dielectric block, said thirteenthcoupling window being defined by a thirteenth area which is not coveredby said third conductive film and having a thirteenth electrode locatedin said thirteenth area; and a fourteenth coupling window disposed onsaid first one of said side surfaces of said fourth dielectric block,said fourteenth coupling window being defined by a fourteenth area whichis not covered by said fourth conductive film and having a fourteenthelectrode located in said fourteenth area; said ninth coupling window ofsaid first dielectric block being in a position corresponding to saidtenth coupling window of said second dielectric block; said ninthelectrode of said first dielectric block being electrically coupled tosaid tenth electrode of said second dielectric block such that signalsfrom said first dielectric resonator are capacitively coupled to saidsecond dielectric resonator; said eleventh coupling window of saidsecond dielectric block being in a position corresponding to saidtwelfth coupling window of said third dielectric block; said eleventhelectrode of said second dielectric block being electrically coupled tosaid twelfth electrode of said third dielectric block such that signalsfrom said second dielectric resonator are capacitively coupled to saidthird dielectric resonator; said thirteenth coupling window of saidthird dielectric block being in a position corresponding to saidfourteenth coupling window of said fourth dielectric block; saidthirteenth electrode of said third dielectric block being electricallycoupled to said fourteenth electrode of said fourth dielectric blocksuch that signals from said third dielectric resonator are capacitivelycoupled to said fourth dielectric resonator.
 24. The filter of claim 1wherein said through bore of said first dielectric block has open endsat said first and second end faces thereof.
 25. The filter according toclaim 24, wherein said through bore of said second dielectric block hasopen ends at said first and second end faces thereof.
 26. The filter ofclaim 1, wherein said ring shaped areas define respective straycapacitances.
 27. A dielectric filter comprising:a first dielectricblock having a through bore extending between first and second end facesthereof, said first dielectric block having a plurality of side surfacesextending between said end faces, each of said side surface lying in arespective plane, substantially all of the surface area of said endfaces, said side surfaces and said bore being covered with a firstconductive film to define a first dielectric resonator; a first couplingwindow disposed on a first one of said side surfaces of said firstdielectric block, said first coupling window being defined by a firstarea which is not covered by said first conductive film and having afirst electrode located in said first area for providing capacitivecoupling between an input signal applied to said first electrode andsaid first dielectric resonator; a second coupling window disposed on asecond one of said side surfaces of said first dielectric block, saidsecond coupling window being defined by a second area which is notcovered by said first conductive film and having a second electrodelocated in said second area; a second dielectric block having a throughbore extending between first and second end faces thereof, said seconddielectric block having a plurality of side surfaces extending betweensaid end faces, each of said side surfaces lying in a respective plane,substantially all of the surface area of said end faces, said sidesurfaces and said bore being covered with a second conductive film todefine a second dielectric resonator; a third coupling window disposedon a first one of said side surfaces of said second dielectric block,said third coupling window being defined by a third area which is notcovered by said second conductive film and having a third electrodelocated in said third area; a fourth coupling window disposed on asecond one of said side surfaces of said second dielectric block, saidfourth coupling window being defined by a fourth area which is notcovered by said second conductive film and having a fourth electrodelocated in said fourth area; said first one of said side surfaces ofsaid second dielectric block abutting said second one of said sidesurfaces of said first dielectric block; said second coupling window ofsaid first dielectric block being in a position corresponding to saidthird coupling window of said second dielectric block; said secondelectrode of said first dielectric block being electrically coupled tosaid third electrode of said second dielectric block such that signalsfrom said first dielectric resonator are capacitively coupled to saidsecond dielectric resonator; a fifth coupling window disposed on saidsecond one of said side surfaces of said first dielectric block, saidfifth coupling window being defined by a fifth area which is not coveredby said first conductive film and having a fifth electrode located insaid fifth area; and a sixth coupling window disposed on said first oneof said side surfaces of said second dielectric block, said sixthcoupling window being defined by a sixth area which is not covered bysaid second conductive film and having a sixth electrode located in saidsixth area; said fifth coupling window of said first dielectric blockbeing in a position corresponding to said sixth coupling window of saidsecond dielectric block; said fifth electrode of said first dielectricblock being electrically coupled to said sixth electrode of said seconddielectric block such that signals from said first dielectric resonatorare capacitively coupled to said second dielectric resonator.
 28. Atransceiver comprising:a pair of filters; a transmission circuit; areceiver circuit; and an antenna; a first of said filters beingconnected in series between said transmission circuit and said antenna,a second of said filters being connected in series between said receivercircuit and said antenna, at least one of said filters being adielectric filter having a first resonator, a second resonator and atleast one inter-stage resonator disposed between said first and secondresonators, said dielectric filter comprising:a first dielectric blockhaving a through bore extending between first and second end facesthereof, said first dielectric block having a plurality of side surfaceslying in a respective plane, substantially all of the surface area ofsaid end faces, said side surfaces and said bore being covered with afirst conductive film to define said first resonator; a first couplingwindow disposed on a first one of said side surfaces of said firstdielectric block, said first coupling window being defined by a firstarea which is not covered by said first conductive film and having afirst electrode located in said first area for providing capacitivecoupling between an input signal applied to said first input electrodeand said first resonator; a second coupling window disposed on a secondone of said side surfaces of said first dielectric block, said secondcoupling window being defined by a second area which is not covered bysaid first conductive film and having a second electrode located in saidsecond area; a second dielectric block having a through bore extendingbetween first and second end faces thereof, said second dielectric blockhaving a plurality of side surfaces extending between said end faces,each of said side surfaces lying in a respective plane, substantiallyall of the surface area of said end faces, said side surfaces and saidbore being covered with a second conductive film to define said secondresonator; a third coupling window disposed on a first one of said sidesurfaces of said second dielectric block, said third coupling windowbeing defined by a third area which is not covered by said secondconductive film and having a third electrode located in said third area;and a fourth coupling window disposed on a second one of said sidesurfaces of said second dielectric block, said fourth coupling windowbeing defined by a fourth area which is not covered by said secondconductive film and having a fourth electrode located in said fourtharea; a third dielectric block having a through bore extending betweenfirst and second end faces thereof, said third dielectric block having aplurality of side surfaces extending between said end faces, each ofsaid side surfaces lying in a respective plane, substantially all of thesurface area of said end faces, said side surfaces and said bore beingcovered with a third conductive film to define said inter-stageresonator; a fifth coupling window disposed on a first one of said sidesurfaces of said third dielectric block, said fifth coupling windowbeing defined by a fifth area which is not covered by said thirdconductive film and having a fifth electrode located in said fifth area;and a sixth coupling window disposed on a second one of said sidesurfaces of said third dielectric block, said sixth coupling windowbeing defined by a sixth area which is not covered by said thirdconductive film and having a sixth electrode located in said sixth area;said first one of said side surfaces of said third dielectric blockabutting said second one of said side surfaces of said first dielectricblock; said second coupling window of said first dielectric block beingin a position corresponding to said fifth coupling window of said thirddielectric block; said second electrode of said first dielectric blockbeing electrically coupled to said fifth electrode of said thirddielectric block such that signals from said first dielectric resonatorare capacitively coupled to said third dielectric resonator; said sixthelectrode of said third dielectric block coupling said inter-stageresonator to a resonator in a succeeding stage; and each of said secondand fifth electrodes being substantially completely surrounded andthereby shielded by said first and third conductive films, respectively,on said abutting side faces of said first and third dielectric blocks.29. A transceiver comprising:a pair of filters; a transmission circuit;a receiver circuit; and an antenna; a first of said filters beingconnected in series between said transmission circuit and said antenna,a second of said filters being connected in series between said receivercircuit and said antenna, at least one of said filters being adielectric filter having a first resonator, a second resonator and atleast one inter-stage resonator disposed between said first and secondresonators, said dielectric filter comprising:a first dielectric blockhaving a through bore extending between first and second end facesthereof, said first dielectric block having a plurality of side surfaceslying in a respective plane, substantially all of the surface area ofsaid end faces, said side surfaces and said bore being covered with afirst conductive film to define said first resonator; a first couplingwindow disposed on a first one of said side surfaces of said firstdielectric block, said first coupling window being defined by a firstarea which is not covered by said first conductive film and having afirst electrode located in said first area for providing capacitivecoupling between an input signal applied to said first input electrodeand said first resonator; a second coupling window disposed on a secondone of said side surfaces of said first dielectric block, said secondcoupling window being defined by a second area which is not covered bysaid first conductive film and having a second electrode located in saidsecond area; a second dielectric block having a through bore extendingbetween first and second end faces thereof, said second dielectric blockhaving a plurality of side surfaces extending between said end faces,each of said side surfaces lying in a respective plane, substantiallyall of the surface area of said end faces, said side surfaces and saidbore being covered with a second conductive film to define said secondresonator; a third coupling window disposed on a first one of said sidesurfaces of said second dielectric block, said third coupling windowbeing defined by a third area which is not covered by said secondconductive film and having a third electrode located in said third area;and a fourth coupling window disposed on a second one of said sidesurfaces of said second dielectric block, said fourth coupling windowbeing defined by a fourth area which is not covered by said secondconductive film and having a fourth electrode located in said fourtharea; a third dielectric block having a through bore extending betweenfirst and second end faces thereof, said third dielectric block having aplurality of side surfaces extending between said end faces, each ofsaid side surfaces lying in a respective plane, substantially all of thesurface area of said end faces, said side surfaces and said bore beingcovered with a third conductive film to define said inter-stageresonator; a fifth coupling window disposed on a first one of said sidesurfaces of said third dielectric block, said fifth coupling windowbeing defined by a fifth area which is not covered by said thirdconductive film and having a fifth electrode located in said fifth area;and a sixth coupling window disposed on a second one of said sidesurfaces of said third dielectric block, said sixth coupling windowbeing defined by a sixth area which is not covered by said thirdconductive film and having a sixth electrode located in said sixth area;said first one of said side surfaces of said third dielectric blockabutting said second one of said side surfaces of said first dielectricblock; said third coupling window of said second dielectric block beingelectrically coupled to said fifth electrode of said third dielectricblock such that signals from said third dielectric resonator arecapacitively coupled to said second dielectric resonator; said sixthelectrode coupling said inter-stage resonator to a resonator in apreceding stage; and each of said third and fifth electrodes beingsubstantially completely surrounded and thereby shielded by said secondand third conductive films, respectively, on said abutting side faces ofsaid second and third dielectric blocks.
 30. A dielectric filter,comprising:a first dielectric block having a through bore extendingbetween first and second end faces thereof, said first dielectric blockhaving a plurality of side surfaces extending between said end faces,each of said side surfaces lying in a respective plane, substantiallyall of the surface area of said end faces, said side surfaces and saidbore being covered with a first conductive film to define a firstdielectric resonator; a first coupling window disposed on a first one ofsaid side surfaces of said first dielectric block, said first couplingwindow being defined by a first area which is not covered by said firstconductive film and having a first input electrode located in said firstarea for providing capacitive coupling between an input signal appliedto said first input electrode and said first dielectric resonator; asecond coupling window disposed on a second one of said side surfaces ofsaid first dielectric block, said second coupling window being definedby a second area which is not covered by said first conductive film andhaving a second electrode located in said second area; a seconddielectric block having a through bore extending between first andsecond end faces thereof, said second dielectric block having aplurality of side surfaces extending between said end faces, each ofsaid side surfaces lying in a respective plane, substantially all of thesurface area of said end faces, said side surfaces and said bore beingcovered with a second conductive film to define a second dielectricresonator; a third coupling window disposed on a first one of said sidesurfaces of said second dielectric block, said third coupling windowbeing defined by a third area which is not covered by said secondconductive film and having a third electrode located in said third area;and a fourth coupling window disposed on a second one of said sidesurfaces of said second dielectric block, said fourth coupling windowbeing defined by a fourth area which is not covered by said secondconductive film and having a fourth electrode located in said fourtharea; said first one of said side surfaces of said second dielectricblock abutting said second one of said side surfaces of said firstdielectric block; said second coupling window of said first dielectricblock being in a position corresponding to said third coupling window ofsaid second dielectric block; said second electrode of said firstdielectric block being electrically coupled to said third electrode ofsaid second dielectric block such that signals from said firstdielectric resonator are capacitively coupled to said second dielectricresonator; and each of said second and third electrodes beingsubstantially completely surrounded and thereby shielded by said firstand second conductive films, respectively, on said abutting side facesof said first and second dielectric blocks.
 31. The filter of claim 30,wherein said fourth electrode is an output electrode for an outputsignal coupled to said fourth electrode.
 32. The filter of claim 1,wherein said second coupling window associated with said firstdielectric block is disposed at a substantially maximum energy locationassociated with an electric field of said first dielectric block. 33.The filter of claim 1, wherein said third coupling window associatedwith said second dielectric block is disposed at a substantially maximumenergy location associated with an electric field of said seconddielectric block.
 34. The filter of claim 30, wherein said side surfacesof each of said first and second dielectric blocks extend in a directiongenerally parallel to the direction of their respective through bores.35. A transceiver comprising:a pair of filters; a transmission circuit;a receiver circuit; and an antenna; a first of said filters beingconnected in series between said transmission circuit and said antenna,a second of said filters being connected in series between said receivercircuit and said antenna and at least one of said filters comprising:afirst dielectric block having a through bore extending between first andsecond end faces thereof, said first dielectric block having a pluralityof side surfaces lying in a respective plane, substantially all of thesurface area of said end faces, said side surfaces and said bore beingcovered with a first conductive film to define a first dielectricresonator; a first coupling window disposed on a first one of said sidesurfaces of said first dielectric block, said first coupling windowbeing defined by a first area which is not covered by said firstconductive film and having a first electrode located in said first areafor providing capacitive coupling between an input signal applied tosaid first input electrode and said first dielectric resonator; a secondcoupling window disposed on a second one of said side surfaces of saidfirst dielectric block, said second coupling window being defined by asecond area which is not covered by said first conductive film andhaving a second electrode located in said second area; a seconddielectric block having a through bore extending between first andsecond end faces thereof, said second dielectric block having aplurality of side surfaces extending between said end faces, each ofsaid side surfaces lying in a respective plane, substantially all of thesurface area of said end faces, said side surfaces and said bore beingcovered with a second conductive film to define a second dielectricresonator; a third coupling window disposed on a first one of said sidesurfaces of said second dielectric block, said third coupling windowbeing defined by a third area which is not covered by said secondconductive film and having a third electrode located in said third area;and a fourth coupling window disposed on a second one of said sidesurfaces of said second dielectric block, said fourth coupling windowbeing defined by a fourth area which is not covered by said secondconductive film and having a fourth electrode located in said fourtharea; said first one of said side surfaces of said second dielectricblock abutting said second one of said side surfaces of said firstdielectric block; said second coupling window of said first dielectricblock being in a position corresponding to said third coupling window ofsaid second dielectric block; said second electrode of said firstdielectric block being electrically coupled to said third electrode ofsaid second dielectric block such that signals from said firstdielectric resonator are capacitively coupled to said second dielectricresonator; and each of said second and third electrodes beingsubstantially completely surrounded and thereby shielded by said firstand second conductive films, respectively, on said abutting side facesof said first and second dielectric blocks.